This is a two-fight chain. The mutated whale does not come off a lure. You must kill a normal Bowhead Whale first and throw that body into the summit crater. Players keep wiping because they trigger the fight undergeared, stand under landings, or speed-boat away and despawn the boss. Gear first, throw, sprint, then either hold the volcano or commit to the slow casino kite.

1Unlock the Fish Bucket

2Prepare Before You Spend the Bucket

3Phase 1 - Bowhead Whale

Do not sell or abandon the first whale. The body is the only way to summon the mutated whale. If you lose it, you start over.

4Summon the Mutated Whale

5Phase 2 - Mutated Bowhead Whale

Same slam pattern as phase 1, plus persistent magma pools on the ground, magma spit projectiles, landing slams that can one-shot from full HP, and reports of multi-bounce landings.

If you have food and AR DPS
Hold the volcano
Fight at the volcano if you can read slams. Use camp buildings to break line of sight on landings.
If solo and dying to slams
Casino kite cheese
Get on the boat and lure it slowly toward Island 4's casino. Too fast and it despawns. Wedge it in the casino door pillars, stand inside, and unload. Do not use the boat as cover because it lands on the boat and you die.
Handyman or bare-hands achievement: You do not fist the whole fight. Shoot it down, switch to empty hands, land only the last hit with punches. Switch early so the gun does not steal the kill.

Common Mistakes to Avoid

After the kill: Take the fin to the scientist for the military boat and ending unlock.