The ‘Coast Guard’ challenge is only available on the Watermill map, and requires you defeat each wave before any mob is allowed to cross the river (either on the top or bottom paths). The achievement will only unlock on Insane difficulty, which is made especially hard due to no fewer than three appearances of Redfang Wrathborn (i.e. the Werewolf boss) on waves 10, 15 and 20, and his less-than-fair ability to charge long distances upon taking a hit.

Simply put, this is the hardest achievement of the game, and you shouldn’t attempt it until you have the following:

1. All Skill trees maxed out (Jack takes longer due to his additional skill – if the other 4 Heroes are maxed or close enough then you’ll be fine). This guide will therefore not cover Skill builds
   
   
2. All Hero weapons to at least Level 6 (i.e. two Rune slots at each charge level). If you can get Wylde to Level 7 this is also helpful
   
   
3. Two Hero Strike Legendary Runes
   
   
4. At least 50% of all other Runes at purple Epic quality, with the rest blue (Rare)
   
   
5. Less essential, but you’ll likely have your Forge in the region of 7-10 by this point

Wylde

• Wylde is your most important character for this strategy – he’ll be your Orb farmer and early damage output, whilst his Hero Strike is the key to defeating the Redfang bosses
  
• Cost Reduction and 2x Orb Runes are essential in the early slots
  
• Epic Damage and Hero Strike in the ∞ slot also non-negotiable
  
• The one Epic Range Rune as below should be a minimum

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Barrows

• Your main support; both in general, and for this strategy
  
• We’ll make use of his Shrine in a central location, so lots of Range is important (ideally Epic, but I managed with the below)
  
• Hero Strike is again essential, and Cost Reduction is very helpful for this

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Jack

• Fairly standard ‘damage-Jack’ build
  
• Tweak the Damage/Barrage ratio to taste, but keep the early Range as this will be critical both for guarding the red entrance (bottom left), and keeping the pressure on the top bridge in the first few waves.

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Jane

• Playing to her strengths – lots of Barrage and Attack Speed will help Jane trigger her knockback skill in a pinch
  
• Hero Strike is definitely not essential this time, but if you have the option you can use as a ‘panic button’

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Sam

• Your secondary farmer – two Orb Runes early combined with her Curse skill are very nice support for when you get her (might not be right away, Zombie waves on Watermill were less threatening than other types in my experience)
  
• As with Jack, would highly recommend 2x Range Runes to ensure good path coverage

The default Wylde Shrine on the map might appear to be well positioned, but in practice it falls short on a number of counts. For the Wylde strategy to work, it’s important to limit his movement to the left side of the map once the boss waves start coming, so he’s never too far from his Shrine to activate his boosted Hero Strike. Also, the default position is unfortunately far too close to the Barrier to defend the early waves.

We’ll make the following changes per the screenshot below, in order of importance:

1. Wylde Shrine top left – very important for early waves, and for dealing with every Redfang
   
2. Barrows Shrine in the centre (replacing the default Wylde Shrine). From here, with a few charges and thanks to the Range perks discussed in the ‘Runes’ section above, his support aura will cover all Shrines and Hero positions, whilst his attack range should manage all but the very bottom of the Red path
   
3. Orb Shrine top right – this is where you’ll ‘park’ Jane for most of the run (or Sam/Jack when defending the yellow path, if they’re a higher level)
   
4. Jane Shrine bottom left – but Jane can’t be in two places at once? Right, but reaching this spot takes waaaaaay too long for every other Hero, so Jane is the only real option. Would recommend positioning her here in case of grass-hopping and/or resurrecting Vampires/Werewolves.

The default Range Shrine in the bottom left is very useful; the other one less so… let’s hope we don’t need it! Also use the pic below to properly familiarise yourself with the colour paths for later – red is bottom, green is top left, yellow is top right.

Due to the semi-random nature of the game’s wave generation mechanic, I can only be so specific here as the monster types, skills, and paths will vary, so please bear this in mind! Regardless, in my experience the first 5 waves tend to be the hardest part of the challenge…

The green path is the shortest path and therefore very dangerous, but benefits from Shrine placement and good accessibility even with limited L1 Hero ranges:

• Get Wylde straight on his Shrine and upgrade to L2 to start farming Orbs
  
• Next get Barrows, ideally on his Shrine if he’s in range to attack as you’ll need the extra slowing early on, otherwise near Wylde
  
• Again, waves will vary, but you’ll likely then need Jack to support with Vampires/Skeletons - move back and forth between supporting Wylde near the entrance, and standing next to Barrows to defend the Barrier

Early red waves present a different challenge, the main obstacles being range, and the time-prohibitive bottom Shrine:

• Place Jack on the Range Shrine, and stand Wylde in front of him
  
• Early on you'll want to place Barrows alongside too, but after a few waves you'll hopefully be able to leave him on his Shrine and upgrade as necessary to bring his support aura to cover the bottom 2 Shrines
  
• Place Jane on her Shrine if additional support is required (esp. in first few waves), otherwise place her on the Orb Shrine

Waves 1 & 2 on the yellow path should present the least challenge of the 3 options, but watch out for grass-hoppers taking you by surprise.

• Get Barrows on his Shrine
  
• Get the other Heroes as appropriate for the wave, and line up to be in range when mobs join the path, with someone on Orbs

Don't be afraid to use abilities (esp. Fire Bomb, or a Pope/Poison combo) on groups on the bridge - you'll be relying entirely on Hero Strikes for the boss waves so abilities will become less relevant

• Bring Jane back up to the Orb Shrine if you haven't already, and place any Heroes you don't have yet
  
• Barrows should hopefully be able to stay on his Shrine for good
  
• Ideally you'll spend your upgrades on Jane to increase Orb flow, but gauge the killing power of the team and spend accordingly
  
• Keep an eye on next wave… e.g. if you're almost finished with a yellow wave then send Wylde over so he's ready on his Shrine for as soon as the next green wave comes. Send Jack and Sam to join him soon after, and leave Jane on Orbs to mop up. Jane will be your backup, since you can quickly call her to use her knockback skill if things get a bit hairy…
  
• Upgrade Heroes in turn - you must have Wylde on L5 before the first Redfang, and others should be able to reach 4 or 5 across the board. Make sure you have enough Orbs in reserve to upgrade Wylde at the end of Wave 9… (560 in my case, with 1 Epic Cost Reduction Rune)

• The first boss will come from the red path – leave Wylde on his Shrine and upgrade him to activate his Hero Strike as soon as you see Redfang appear! The Hero Strike benefits from the 50% damage boost of the Shrine.
  
• Important: As long as no Heroes hit Redfang before Wylde's Hero Strike blades reach him, he won't charge and will comfortably die long before reaching the bridge
  
• Move Wylde, Jack & Sam down to defend around the Range Shrine to mop up any survivors. Barrows should have enough range by now to never move from his Shrine, and Jane can hopefully stay on Orbs but be prepared to call her if required! If Wylde has enough range at L6 to fight from his Shrine then by all means leave him there.

You should be comfortable with Hero positioning between waves & paths by now – mainly it will be Sam & Jack who always move, with Jane only moving in emergencies and Wylde only if needed for range.

The 2nd and 3rd bosses follow the green path and are more dangerous than the first, for two reasons:

1. The distance to the Barrier is significantly shorter
   
   
2. Wylde will be in range and hit him immediately when he enters, causing him to charge over the bridge

Therefore, we can't rely on Wylde's Hero Strike alone to catch the boss in time, meaning this time as soon as you spot him you'll instead upgrade Barrows to L6 (560 Orbs) to freeze the boss on the spot, followed by Wylde to L7 (910 Orbs) straight after to bury him. Note there’s a small delay on Barrows’ freeze too, so it’s important to hit it as soon as the boss enters the map!

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• Treat the third and final Redfang exactly the same as the second - this time you'll need 910 + 1470 = 2,380 Orbs (using my setup) to upgrade Barrows to L7 and Wylde to L8
  
• If Wave 19 is on the yellow path, make sure you leave Wylde on his Shrine to fight from a distance so he can activate Hero Strike as soon as possible
  
• The Hero Strike will likely clear the entire final two waves, and victory is yours!

Thanks for reading – hope this guide helps you get the achievement, and let me know any comments/suggestions! 😊