So, in this guide I will describe the easiest way to get 100% achievements in Shad'O. To make your gameplay easier me personnaly recommend to get Stillness, Protection and Boost Coollection spells as soon as possible, as well as complete Nigtmare levels and upgrade your Companions and Spells earlier. Some of the achievements are Story related, some - require specific actions made during the fights - and there are 7 (of 30) achievements you can get diring one battle without any serious problems, I will mention them at the end of the guide.

Great Explorer
Fully explore the William’s memories map.

To get this one, you should complete all the basic battles in the game, but you don't need to complete last one. Achievement will pop up immediately after the last island emerges from the shadow sea.

Blood ties
Save all the memories in nightmare mode.

Simply finish all the battles for the 2nd time in Nightmare mode and the achievement will pop up. The Boss battles don't have Nightmare mode and won't count.

Comfort Eagle
Pass all the special battles.

To get this one you will need to complete all six Special Battles in the game. There are 2 types of these battles : Mystery Card and Energy Issue, 3 of each.

• For Mystery Card: During these battles you will have a choice between two Lvl1 Companions or a Mystery Card, which in turn can contain either a more powerful Lvl2 or Lvl3 companion, or a negative Spell like Freeze, Acid or Shock. To get maximum bonuses - use the Mystery Card first 3-4 times at the beginning and if you get negative result - restart the battle, if you get nice Companions - continue. Try to not use Mystery Card after that at all, since it's more likely you will get a negative spell rather than a companion, and it will ruin your game.
  
• For Energy Issue: During these battles all of your companions are disabled and you can wake up only one at time by clicking on it. This battle type is purely tactical and requires good timing. Still, it should be noted, that if Companion started his action animation (Puncher's punch, Doc's healing or Greedy's attack) - it will finish his move even if disabled in a middle of process. Knowing this will save you precious seconds and will help to complete these battles.

Catch them all!
Unlock all of your companions’ upgrades in the book.

To get this one you will need to complete the Basic and Nightmare battles, thus earning upgrade points and spend them, upgrading your Companions to maximum.

Alakazam
Unlock all the spells in the book.

To get this one you will need to complete the Basic and Nightmare battles, thus earning upgrade points and spend them to obtain all the possible Spells in the game.

Resuscitation
Defeat the first Boss.

This is a Story related achievement and it cannot be missed. The Boss have abilities:

• Spawning Shadows: It will start with weakest Gloomio shadows and the more you will damage the Boss, the stronger the shadows become.
  
• Shock: The Boss will periodically launch a shockwave, disabling all your Companions and damaging them over time. To avoid this attack - watch the boss carefully and use Protection Spell when he starts roaring.

Avoid damaging the Boss early and build a strong defence instead. When you feel youself ready - build some Shooters near the boss and they will finish him relatively fast.

Bodyguard
Defeat the first Boss without letting any of your companions get electrocuted.

You can get this achievement simultaneously with the previous one. To get it you will need a Protection Spell. Watch the Boss carefully and use it every time he starts roaring before electrocut your companions.

Painful memory
Defeat the second Boss.

This is a Story related achievement and it cannot be missed. The Boss have abilities:

• Spawning Shadows: It will start with weakest Gloomio shadows and the more you will damage the Boss, the stronger the shadows become.
  
• Blind: The Boss will periodically launch a shockwave, disabling all your Companions. To avoid this attack - watch the boss carefully and use Protection Spell.
  
• Move: The Boss will move from one spawn point to another.
  
• Crush: After emerging from spawn poing the boss will crush all Companions in front of him.
  
• Grow : After receiving some damage the Boss will grown a little, destroying all Companions built too close to him, getting larger effect area of Crush ability.

Avoid damaging the Boss early and build a strong defence around the Memory instead. When you feel youself ready - start building Shooters near every spawn point, but keep in mind not to build them in front of him and build new ones every time he grows up and destroys some of them.

No harm done!
Defeat the second Boss without using the Doc companion or the "Care" spell.

You can get this achievement simultaneously with the previous one. Getting it may prove itself tricky since the Boss, after getting some damage starts spawning screaming and shooting shadows, destroying your Companions relatively quickly.
The key to success is in building strong defence before attacking the Boss and accumulating some Light resource to build the Shooters attacking the Boss fast and destroy him before his shadows destroys your Memory.

Moment of truth
Defeat the last Boss.

This is a Story related achievement and it cannot be missed. This Boss won't spawn any shadows, he's too dangerous for you anyway. The battle can be divided in two stages.

• Stage 1: The Boss is moving around the battlefield, stopping at 3 certain points, shielding himself with Ice Block and starting to directly damage your Memory with beam attack. To break the ice you will need to apply some physical damage, but even Lvl3 Puncher will need 2-3 attacks to do that, so forget about him and Pulsor Companions, using Earthquake Spell instead. Timing is essential during this battle, as well as Lvl3 Mole, providing you with necessary magic resources. Build a couple of Shooters at each side of battlefield and upgrade them as fast as you can. After losing half of his health the Boss starts using WhirlWind ability sometimes, damaging nearby Companions, so try to finish him fast. Be warned, that after his "death" the Boss will respawn and attack you again.
  
• Stage 2: The Boss will respawn at the place you killed him, destroying all nearby Companions and starting to attack your memory without a chance to be interrupted. Build Shooters around him as fast as you can. You can sell the other Companions to build more near him. Remember that you can always heal your Memory with Sacrifice Spell, but by doing so you will lose Puffed Out achievement. You can still beat the Boss without using it at all.

Puffed out
Defeat the third Boss without using the "Sacrifice" spell.

To get this achievement read the Boss fight tactics above. Use the Mole to get magic resources and use Earthquake Spell as soon as Boss starts attacking your Memory. You must have at least half of Memory's health before 2nd stage of battle.

Hearty trencherman
Win "The endless corridor" battle using only Collector and Greedy companions. (Spells are allowed)

Since you'll get Greedy Companion after beating 2nd Boss, you will need to complete this one at Nightmare battle. Still, it's not hard at all. Start with Collectors, then build as much Greedy Companions as you can. Do not upgrade them, only build. The Stillness Spell is really useful too.

Rainbow Warrior
Win "The slabs waterfall" battle using only Collector and Rainbow companions. (Spells are allowed)

Since you will get Rainbow Companion after 1st Boss battle, you will need to complete Nightmare battle level for that one. Start with building Collectors, then build as much Rainbows as you can. Do not upgrade them, only build. Use Stillness Spell in difficult situations.

Get physical
Win the "Underneath the Christmas tree" battle using only Collector and Pulsor companions. (Spells are allowed)

Since you will get Pulsor Companion after 2nd Boss battle, you will need to complete Nightmare level for this one. Start with Collectors, then build as much Pulsors as you can. Upgrading them can help, but remember that since you can't use Pucher to slow the enemies - most of them will pass your Pulsors faster than they can reload, so it's advisable to simply build more Pulsors. Using the Stillness spell is helping too.

Sadist
Make it so that 4 Collector companions get destroyed in "The snowmen’s waltz" battle.

During this battle will be introduced a new, poisonous shadow, which, after receiving Puncher's punch will cover with gas and damage all the Companions nearby. Simply build 2-3 Punchers near the Collectors and they will be destroyed in 1-2 waves.
Warning: The achievement description lacks the important detail - you must WIN the battle after losing companions.

Short range
Win the "Dark woods" battle without using any range boost locations.

The battle is quite difficult itself and without Range Boosters it will become even more difficult, so its advisable to get this achievement during the 1st, Basic battle. Cover the passages with Projectors and Rainbows, and don't forget about Protection Spell when exploding Gloomio's appear.

Diet!
Win the "Ice trap" battle without using the Greedy companion.

To be honest, this battle can be won without Greedy Companions at both Basic and Nightmare modes. At the start of battle use Go Through The Fog spell and build your defences at crossroads near the Memory. Start with some Rainbows, add Lvl3 Punchers, 2 at each of the paths, then 5-6 Pulsors at each path and cover them all with Docs. Use Earthquake on Armored Giants and Stillness during massive waves, and don't forget to Boost the Collection spell and upgrade your companions in time. The Lvl3 Mole is also quite useful.

Minesweeper
Destroy 10 "Bomb" shadows before they explode.

The Bomb shadows will appear for the 1st time during Lights on the Town battle. Build your defences well and destroy 10 of them before explosion and you will get this achievement easily.

Easter!
Gulp a dozen "Shell" shadows down with your Greedy companions.

The Shell shadows will appear for the first time at Cushion Mountain battle, after the 2nd wave. Start with building Collectors, then build as much Greedys as you can. Despite the fact that devouring a Shell will damage the Greedy, you can ignore that and simply build new ones, because you don't need to win a battle, just devour 12 Shells.

Rescue team
Watch the credits till the end.

Complete the game and watch the end credits till the end. Don't worry, it will take just a couple of minutes.

Spring cleaning
Kill 1000 enemies.


Exterminator
Kill 2500 enemies.


Shadow Killer
Kill 5000 enemies.

These 3 are easy ones, you can get them during your playthrough. If you are completing Nightmare levels too, you will get the last one, Shadow Killer, long before the end of game.

War Chief
Use 10 different companions during a battle and win it.


Moneywise
Sell 30 companions during a battle and win it.


Thrifty
Reach 1000 light resource in any battle.


Pinchpenny
Reach 2500 light resource in any battle.


Mana fountain
Get 250 magic resource in any battle.


Sorcerer's Apprentice
Cast 20 spells during a battle and win it.


Fireworks
Cast at least once each 10 spells during a battle and win it.

The easiest way to get all of these ones is replaying the 1st Boss battle.
Start with Collectors and build a defence, but do not damage the Boss. Then build a Lvl3 Mole and start digging, until you get 250 shadow fragments and Mana Fountain. After that use Boost the Collection spell until you get 2500 Light and both Thrifty and Pinchpenny achievements. Start building and selling (and counting) new companions, until you sell 30 of them. After that build one of each possible Companions and use one of each possible Spells. If you protected your companions with Protection spell, you will get 20 spell counter at this time too. Finish the battle and Moneywise, War Chief, Sorcerer's Apprentice and Fireworks will pop up.