How the mutated whale spawns
It is not fished: the dead Bowhead Whale thrown into the volcano turns into it.
- Kill the Bowhead Whale and carry the body up to the volcano rim.
- Throw it into the crater; the eruption spawns the mutated whale about three seconds later.
- Go back down the mountain to open ground near the camp before fighting.
How to kill the final boss
Same rule as the first whale, plus magma and a new jump pattern at half health.
- Stay under it and fire while it is on the ground; run when it launches.
- It spits magma that leaves lava pools: step off any spot where lava appears.
- From half health it bounces three times in a row. Run far when it goes up and count all three landings before turning back.
- Heal from the fish you laid out before the fight, and get the rifle back up immediately after eating.
- Stay around the volcano slopes and the camp: pulling it out to open sea can reset the encounter.
Final boss solo and in co-op
Solo it is a long fight; keep plenty of food on the ground before you start.
Two to four players make it the easiest it gets. On Hard (added in 1.0.9) it has 25% more health.
For the bare-hands Handyman achievement, plan the last hit before the fight starts.
Assault Rifle or Dynamite for the final boss
A fully equipped Assault Rifle is the standard weapon.
Dynamite is viable: patch 1.0.12 made the whale take blast damage on tail landings as well. Speedrunners split about 21 to 25 sticks between two piles; since 1.0.11 your own blast can kill you, so step clear first.
Mutated Bowhead Whale health
The Mutated Bowhead Whale has 38,000 health on Normal (75% on Easy, 125% on Hard).
What to do after killing the mutated whale
Among the $5,000 meat chunks lies the Whale Fin, pale with a glowing crack; it is the only drop that ends the game.
Give the fin to the scientist, take the military boat keys and press E on "Get back to the mainland". After the credits you wake up on Island 1 with your boat and can keep playing.