Super short guide - super short intro. I found some levels pretty challenging, so it's a bit annoying there are no guides. I'm not a pro player by any means, but Insane doesn't seem much different to Normal difficulty, hopefully this guide will help you achieve Deathless on Insane, or just make the levels more manageable if you have no one to co-op with.

What the guide won't cover:

• Specific placement of "Towers" unless it's helpful
  
• Specific spawn timings of waves, again unless it's helpful (mass slimes)
  
• Specific upgrades required (though I will rate my favourite Towers)
  
• Location of all relics (too hard to describe, too lazy to screenshot)

Change Log 1.4: Updated wording on 6.3 Crypt of Aegis, additional tips after successful run on Insane, added title screen for each level
Change Log 1.3: Updated wording on 5.3 Clarent's Sanctum, additional tips after successful run on Insane, added additional tips on healing with Kaiim's draw skill
Change Log 1.2: Updated wording on 4.2 Manasan Village, noted final wave slimes and 4.3 Vaaran Safehouse after successful run on Insane
Change Log 1.1: Updated wording on 3.3 Snowfly Peak, additional tips after successful run on Insane
Change Log 1.0: Created Guide

Each level is rated Easy, Medium, Hard (rated for solo play in my opinion). I'll cover why the level is difficult and what you can do to make life easier as a solo player.

1.1 Exhausted Ruins (Easy)
Rating: Easy because it's a tutorial level, ample resources

• Enemies from right-side only, place Towers right of Ruin

1.2 Eastern Border (Easy)
Rating: Easy because simple waves, adequate resources

• Bomb the bridges to funnel most the enemies to the bottom level
  
• Place Towers to destroy yellow shields, Clu to clean up flyers
  
• Make use of the Defense Block to delay enemies

1.3 Kobo's Objective (Easy)
Rating: Easy because simple waves, adequate resources

• You will need to use Clu's bow or bombs to kill the red slimes
  
• Bart's hammer can block the slimes temporarily
  
• The torches on the top levels will convert all bullets to red fire damage
  
• The level paths change, pretty easy unless you forget about the slimes
  
• Tri-Shots are all you'll really need on this easy level
  
• Multiple red slimes will come out of the top left portal Wave 5, make sure Clu is there with the bow

2.1 Royal Monastery (Easy)
Rating: Easy because simple waves, adequate resources

• Place a Defense Block on the top 2 "buttons", this will keep the top bridges open
  
• If you stay off the mid-tier "buttons", all enemies will funnel to the bottom-level
  
• Wave 5 have red slimes on both sides, drop them down to the spikey brambles
  
• Auto Turret to break shields, Tri-shot will take care of everything else

2.2 Grand Aqueduct (Easy)
Rating: Easy because simple waves, adequate resources despite limited build space

• Raise lifts up to build them away from debris
  
• The stalactites are fairly useless as they hang above your defenses, 2-stack tri-shot will trigger the stalactite if placed on the furthest end of the lift
  
• You may want some Auto Turrets to kill the golems, ie don't convert everything to tri-shot
  
• Bart will struggle to hold the final red slime and golem wave on the right, once you're done clearing red slimes with Clu's bow, pop over to help Bart

2.3 Sunken Bastion (Medium)
Rating: Medium because low resources, though enemies only come from 1 direction, cannons provided have good DPS, but can get trapped using them

• Stack Tri-shots 4 high as close to Kaiim (behind the bottom cannon)
  
• If you place Towers too far forward on the bottom lane, the slope makes it hard to hit
  
• Leave Bart to defend the bottom with Hammer, use Clu to clean up with Bow/Cannon
  
• Be careful of fliers heading toward Kobo
  
• Last wave is a rush of slimes, other enemies will make them hard to hit with Clu's bow, use Bart on the bottom cannon if needed.

3.1 Hallowed Ground (Easy)
Rating: Easy because simple waves, adequate resources

• Use Kaiim to draw resources through the doors
  
• Stack Spirit Traps, using the existing Spirit Trap as a guide
  
• Tri-shots with Torches are all you'll really need

3.2 Forgotten Temple (Easy)
Rating: Easy because simple waves, adequate resources

• Kaiim can draw the top resources without riding the lifts
  
• Tri-shots with Torches are all you'll really need

3.3 Snowfly Peak (Medium)
Rating: Medium because it's the first escort mission, hard if played normally, easy as it can be cheesed by taking advantage of spawn distance to active players. For both methods, you'll want to mainly use Kaiim to run and draw resources, create torch blocks to reach high places, and activate buttons. Use Clu to blow up bridges across brambles to delay/kill the crabs. Upgrading Clu's rifle will be quite useful in killing the blue flyers (snowflys)

Legit Way

• Wave 1: Close the gate, shoot the bridge with Kaiim/Clu's Bow, kill the red caterpillar and 2 blue flyers coming up behind the Caravan
  
• Wave 2: Quickly close the 2nd gate (Kaiim or Bart on top button), quickly drop a platform to reach chips. Place one bowgun and torch on the platform right above the caravan (as close to the edge as possible) - this will be enough to hold them
  
• Wave 3: Activate the button to drop a boulder, push it all the way to the right. Grab the relic and resources and roll the boulder towards Caravan. The Caravan will block the boulder, but you can roll it off the cliff on the right (use it to block the next tunnel). Head back and take care of any creeping enemies - the bowgun and torch should have held the crab far back enough.
  
• Wave 4: Clu with the rifle on the caravan should be enough to handle the enemies, leave Kaiim and Bart to defend as well. Make sure to blow the bridge once you see the unlit torch. Quickly try to run forward with Clu and powershot with the bow to light the 2 unlit torches, grab the yellow base heart and relic. If you are not good with Clu's bow, use Kaiim and orbit the Purple Orbs to light the 2 torches.
  
• Wave 5: You should have enough resources to drop a Tri-shot under both the left and right pipes. It should hold enough to let the caravan through to the next area. If you have enough yellow resource, then Auto-Turret will be better. Alternatively, bowgun for knockback.
  
• Wave 6: This area looks similar to Wave 4 with the stalactites above, but a crab spawns before the spike pit. Either use Clu to drop the stalactites or Bart to kill the first crab. Blow the bridge to the spike pit. Shoot down any blue flyers.
  
• Wave 7: Place 2 Tri-shots on the tree under the boulder. Push the boulder to the right to roll it down the hill. This gets a bit hectic as red beetles will start coming out. Shooting them will make them drop - don't let them drop on the Caravan. Once they're on the ground, the slope makes them hard to kill as well, so use the bow. Blue flyers from Wave 7 will hit the hill and come back towards the Caravan. Best to kill them all with Clu.
  
• Wave 8: The last section has 4 pipes and enemies coming up the hill. The top 2 pipes will spawn enemies that won't hit the Caravan, so ignore those. Leave Kaiim throwing Red orbs off the back of the Caravan while placing tri-shots to shoot at the torches on the pillars. You should have an abundant blue and red resources, so combine them as well to make bounce freeze orbs down the hill.

Cheese Strat

• Create a Blowgun Turret for knockback under the first gate
  
• Close the first gate
  
• Use Kaiim's red orbs to open the first spike trap
  
• Run to the end while grabbing resources and collectables
  
• If you did it right, the Caravan shouldn't be taking any damage, you can set-up for Wave 7 and 8.
  
• Run back towards Amber and defend Wave 7 and 8.

4.1 Badlands (Easy)
Rating: Easy because simple waves, enemies only coming from one direction

• Kaiim is more efficient than Bart to collect resources on this level
  
• Stacking 4 Bowguns and 2 Tri-shot with a torch right next to the Caravan should be enough
  
• Any additional defences can be placed on the mushrooms
  
• Leave Bart blocking at the bottom of the slope
  
• Beware of jumping spiders using the mushrooms to get around your traps

4.2 Manasan Village (Easy)
Rating: Easy because of simple waves and natural choke-points

• Fill defenses where the torches are 2x4 worth of defenses on each side
  
• Once you've filled those, start by placing bowguns 2 platforms above the door (same level as the red mushroom)
  
• Last wave is practically all slimes, Clu bow spam should help, if you're worried drop a few extra mines around

4.3 Vaaran Safehouse (Medium)
Rating: Medium due to the size of the map, it's not too difficult to defend both sides but takes time to collect resources due to the slow spawn rate of the bubbles and large distance of the map.

• The top left pipe mainly produces red grenade launching enemies - a torch and turret will hold this for most the waves with repairs every now and then. The same goes for the top right pipe. On the 4th wave purple enemies may destroy these turrets.
  
• The left defence should be built as close to Zula as possible, mainly bowgun and tri-shot with torch. Add blue Dragon Turrets to the tiny platform left of the closest mushroom platform.
  
• The right defence should be built as close to the 3 Vaaran's as possible, mainly bowgun and tri-shot with torch. Add blue Dragon Turrets to the doorway (tiny platform) right of the closest mushroom platform.
  
• The only enemies to watch out for are the yellow jumping spiders, if hit at a certain spot they will jump to the upper mushroom platform and potentially land on or behind your Towers
  
• Place turrets on the edge of the mushrooms, bowguns and dragon turrets' downwards shots will hit enemies below.
  
• Watch the glow from above, this is where the large spider spawns. Eggs will hatch spiders when hit, or if left alone all spiders will be released at once. It is your choice if you want to put a turret near these spawn spots - it's not necessary if you stack defences near the left and right bandits.

5.1 Plain of Kevi (Easy)
Rating: Easy due to simple waves and being able to start this level with max resources; before starting this level, buy the level 1 resource generator for the 4 colour resources.

• Before starting the fight, use Zula to set up resource generators for each colour (multiple if possible) - except there are no yellows resources until the waves start. This will give you a way to have a lot of resources to start despite the scarce resource spots around the map. Be careful not to place the generators where you want to place Towers, and not to place them too close together as it becomes difficult to accurately collect, 1 generator of each colour will spawn at the start of the waves next to the cages.
  
• The waves are fairly simple, just place defences in front of the cages - since you have so many resources it's very easy to defend
  
• Only thing to worry about are Purple Slimes - when hit they drop smaller yellow slimes. Zula should be able to hold the right side by herself
  
• The practically unlimited Blue resources mean that you can practically complete this level using only mines and Bart blocking

5.2 Cracked Catacombs (Hard)
Rating: Hard due to not be able to cheese the second escort mission and having a wide variety of enemies (Purple Indra Soldier). This also requires fast coordination between "follow me/stay here" function and flicking between characters. Before you start, I highly recommend buying Zula's bomb for 500.

• Wave 1: Before activating the lift, collect the resources, yellow base heart and the relic. Once you activate the lift, destroy the boulder manually to give you more time. Jump up and push the keyblock over the collapsing bridge. Ignore the blue flyers in front of the drill, they will die. Continue to the next area, destroy the boulder manually and get the 2nd relic using the keyblock. Retrieve the red and purple resource, return to the Drill.
  
• Wave 2: By now, the Wave 1 enemies will be gaining slowly on the drill, with Wave 2 starting. You can manually kill Wave 1 enemies with Bart blocking, Kaiim on Purple, Clu on Rifle, and manually using Zula to bomb. Then quickly jump to the 2nd level (under the keyblock, place a Defense Block and Bowgun Turret. Quickly lower the drill to the next area.
  
• Wave 3: Manually destroy the boulder and using Clu, push the keyblock to the right and blow up the bridge. Bart, Kaiim and Zula should be able to hold the bottom lane, use Clu to set off the laser.
  
• Wave 4: Run forward with Kaiim and push the 2 keyblocks, throw a red orb through the gap to kill the purple bug. Place a Torch Block right under the Life Flower above the lift, then run back and leave Kaiim beneath the bridge to use Purple Orbs. Place a slow next to Kaiim with Zula, and then leave Zula on the same platform as the Life Flower throwing Bombs. Place Bart to the right of where Zula's bombs land. Use Clu to shoot Rifle through the Torch Block towards Bart and the Wave 4 enemies. If Bart is disabled, switch to him and drop a defense block quickly, then switch back out. Once the lift can be activated, do so and recall all characters.
  
• Wave 5: The Torch Block should stay floating, and the grenades from red enemies will fall into the gap, killing many Wave 5 enemies. Leave Kaiim with Purple Orbs right next to the wall, further delaying Wave 5. You can leave Zula at the top of the wall with Bombs to also help kill enemies. Using Clu, run forward and push the keyblock to unlock the cannon.
  
• Wave 6: By now, Wave 6 will start so recall everyone. Place a Bowgun and Torch on the edge of the lift, with Bart blocking. Set Kaiim on the cannon, Clu using Rifle behind the Torch. Bring everyone back to the platform behind the Torch Block before lowering the platform on the drill.
  
• Wave 7: Once you lower the platform, use Zula to dash up to kill the purple bug. Drop down and manually destroy the boulder. Your team may be disabled, recall them and leave them under the platform where the Life Flower was.
  
• Wave 8: Once Wave 8 starts, run forward and lower the cannon. Place Kaiim with Purple Orbs under the bottom tunnel and Zula with Bombs on the top wall, this will delay the enemy from destroying the wall. Use the cannons and the same delaying tactics. If you have extra resources, Clu's mines will help take care of the slimes.

5.3 Clarent's Sanctum (Hard)
Rating: Hard due to number of difficult enemies and positioning of resources. For me this was the hardest level to get all collectables and resources while protecting the Clarent.

• The level starts with a purple resource spawner, make a Yellow and Red Resource Spawner ASAP (I would place on the head)
  
• Enemies can walk across the top of the Clarent without damaging it, leave Kobos here
  
• Zula's Bombs are effective at clearing the spike balls quickly
  
• Place a stack of Yellow Turrets directly next to Kobo first, 1 Torch Block. Use Bart to protect these (there are not many blue enemies until Wave 7, Clu and Dragon Turrets should be able to handle them)
  
• Place Bowgun and Dragon Turrets below the cannons on each side as well as on the head of the Clarent
  
• Blue Slimes appear on Wave 7, clear them quickly with Clu before they reach your Towers
  
• Purple Slimes appear on Wave 8, make sure to set Kaiim to Purple Orbs and manually use Zula to switch between Shuriken and Bomb attacks.

6.1 Hozai's Vault (Medium)
Rating: Medium due to no blue damage, the teleporters might make it seem difficult, but really there are only 2 platforms on each side to defend. You won't have access to Clu, but you can again max out your resources before the defence mission begins.

• Resources are limited in the level, set-up resource spawners
  
• Begin by placing Towers as close to the centre as you can (where Kobo was)
  
• Then begin by placing Towers towards the end of the middle tier (above the Clarent's shoulders)
  
• Be careful of enemies falling onto the shoulder jumping over your bottom tier Towers
  
• Blue enemies will be difficult without Clu, make use of Bowgun Turrets, Yellow Turrets and Kobos
  
• Make use of Bart's blocking abilities to stop the slimes from killing your towers

6.2 Sunken Crater (Easy)
Rating: Easy due to level layout being quite helpful despite only having Clu

• Spike trap everywhere
  
• Placing a spike trap on a damaged spike trap, will upgrade it and give it full health
  
• I recommend NOT upgrading the Torch Block to Dragon Turrets and NOT upgrading the Defence Block to Trishot, this gives you more control of the falling platforms
  
• Place mines next to the slow traps as a last line of defence against the purple slimes

6.3 Crypt of Aegis (Medium)
Rating: Medium due to initial limited resources, but relatively easy once your choke points are identified and filled with Torch Block, 2x Bowgun, 2x Trishot, Ghost.

• NOT CONFIRMED: There is a turret limit (I want to say 40 or so Turrets) I noticed some turrets disappear after placing some additional defences. This can really screw your choke points so be careful.
  
• Do not waste bombs to blow up the bridges, yellow flyers and red bugs will blow them up with their own bombs
  
• Zula can defend the 1st wave by herself, there is a timing overlap from left to right, so use Bart to delay the second side
  
• Clu can defend the 2nd wave, with the help of Bart removing shields
  
• It's important to get a yellow and red resource generators ASAP
  
• Setup some delaying defences (Bowgun and Defense Block) next to Kobo, you shouldn't need these, but it's a just in case
  
• When Wave 5 starts, stacking 4-5 Towers right where the teleport takes you (under the wooden platform) will be enough to defend with Bart
  
• The rest of the waves are pretty straight forward once the other coloured doors are unlocked
  
• This is doable without activating Aegis
  
• The resources behind the coloured doors are not worth collecting

I've seen some gameplay on YouTube and most don't make use of all the gameplay mechanics effectively. Below is also a quick overview of each 'tower' and weapon (I won't repeat any in-game flavour text) and when/how to use them. I've rated them out of 5.

Gameplay Tips

• Clu's bow and the Bowgun shot arcs down, so will allow you to more effectively shoot down slopes
  
• Shovel instant mines resources, get this ASAP
  
• Bart to mine 2 resources close together, Kaiim to mine only when 3+ resources are spread apart
  
• Bart blocks with his weapons automatically, and repairs damaged Towers in range automatically. Placing him in front of the Towers will allow him to block until he gets pushed back, where he then switches to repair mode
  
• Kaiim's Red and Purple orbs circle around him when attack is held down. They can catch fire as they pass through a torch, this is a much easier way to light unlit torches without using a Torch Block
  
• Kaiim's Purple Orbs circle at a much greater distance than the Red Orbs; DPS is also quite good, placing him under/over platforms to auto attack is useful, placing a torch on the path of the purple orb will make him effective against Red and Purple enemies
  
• Kaiim's resource collection skill works on chips and hearts as well; make sure you use this especially on big waves of small enemies so you don't have to run out to collect chips or if you're losing health and there are a few hearts lying around
  
• Zula's Boomerang has a pull effect, placing her away from the base/flanking the enemy has the added effect of delaying them slightly
  
• Zula's Bombs have a slight knock-back effect and great splash damage, useful to use to hold choke-points

Turret

• Defense Block 4/5
  The Defense Block is useful before you get Kaiim, when the Torch Block becomes available. At max health, it only has 10 more health than the Torch Block. Used to delay monsters while your damage dealing heroes are not nearby
  
• Auto Turret 3/5
  The first Turret you get, it gets the job done and will be required as a yellow damage dealer to break shields
  
• Bomb 5/5
  For 1 blue resource, the damage is good to have around. If you're very desperate, you can drop this next to the base
  
• Spike Trap 2/5
  You will use this every now and then, but considering it uses 2 blue resources, I feel you're better off making a Tri-Shot Turret or a Dragon Turret with your blue resources.
  
• Tri-Shot Turret 5/5
  Probably the most used Turret. The spread fire and the blue & yellow damage make this almost a no-brainer. Throw a Torch Block next to this and you also do red damage with the chance to burn.
  
• Blight Trap 1/5
  An upgrade to the Spike Trap, while the Blight Damage is good, you're using up yet another Blue resource. Playing solo means you're trying to manage your resource gathering time, tying up Bart to repair Spike and Blight Traps is not a good use of time
  
• Vanguard Turret 2/5
  The yellow resource will be your most used: Tri-Shot, Bowgun and Auto-Turret. I wouldn't make Vanguard Turrets unless I had the extra resources.. I'd much prefer an additional Tri-Shot or Bowgun
  
• Spirit Turret 1/5
  The range on the spirit turret is quite short and the damage is not great. There aren't many levels where you can place this without it being damaged. Similarly I place this in the category of the Spike and Blight Trap
  
• Torch Block 5/5
  The perfect addition to any defence group; place next to Tri-Shot, Bowgun and Auto-Turret to add fire and red damage
  
• Bowgun Turret 5/5
  The knockback on these are great, and having more than 2 staggered will create a rain of knockback arrows. The fall-off distance will also mean you can aim them at lower levels from quite high up
  
• Dragon Turret 5/5
  The freeze effect is good but random, what's useful about this is the bounce factor which will allow it to roll down hills and off platforms.
  
• Lion Turret 2/5
  The upgraded Spirit Turret has much better range, which does allow it to be placed in more places without being damaged. Having said that, you're giving up a Torch or Bowgun to place this. If you've already wasted on a Spirit Turret, you can double-down.
  
• Shroom Generator 2/5
  All generators: useful for 3 levels where resources are low, otherwise fairly useless
  
• Flower Generator 2/5
  All generators: useful for 3 levels where resources are low, otherwise fairly useless
  
• Slow Field 3/5
  Fairly good at slowing enemies. Unlike the Defence Block, it won't stop enemies, but because it generates a field, you can place it somewhere where it won't get damaged
  
• Kobo 3/5
  The only purple damage dealing turret, there's not as much utility as any other damage dealing turret. Having said that, there's not many combinations worth spending purple resources on
  
• Orb Generator 2/5
  All generators: useful for 3 levels where resources are low, otherwise fairly useless
  
• Ore Generator 2/5
  All generators: useful for 3 levels where resources are low, otherwise fairly useless

Weapon
Each weapon has 3 level upgrades that can be purchased. 3 weapons are marked 9999 chips, these are obtained through the special missions for each character other than Clu.

• Hammer
  See placement in gameplay tips above
  
• Shovel
  See resource gathering in gameplay tips above
  
• Rifle
  Upgrading to 3rd Tier gives you piercing bullets. This is quite useful for later levels where lots of enemies stack up
  
• Bow
  Upgrading to 3rd Tier gives you 2 shots at once. The damage is split between the two arrows, so you don't get double damage, though you do get double the crit chance.
  
• Fire Staff
  Upgrading to 3rd Tier will make this automatically on fire, thereby not requiring to use a block to orbit fire around you
  
• Orbital Staff
  Highest upgrade gives you 4 orbs, based on the distance and speed of rotation this is worth getting
  
• Shuriken
  Has a pull effect which can be useful; the delay return is only really useful during the exploration parts of the level
  
• Sticky Bomb
  Great DPS, see gameplay tips above