Angler McCoy is a challenge in Whiplash Rapids. It is unlocked by killing all sixteen piranhas. They are all split up unevenly across the 4 main Areas of the level (not counting the Rumble or Hangman Arenas). Here is a guide to find all 16 of them:
Location of the Piranhas[]
Piranha 1 (Area 1): The first Piranha can be seen under the platform with the first Skull Switch and a Harpoon Gun Enemigo.
Piranha 2 (Area 1): The second one can be found close, near the first Red Platform you see.
Piranha 3 (Area 1): The third one can be found to the left of the second one, near the Gatling Gun Enemigo.
Piranha 4 (Area 3): In the water you'd jump into the get the 1st Chest, you'll find the fourth Piranha. A whip or gun can be used to reach it if you don't want to jump into the water.
Piranha 5 (Area 3): Between the three boulders that drop down when pressing the TNT Plunger.
Piranha 6-7 (Area 3): Can be found right after the fifth one.
Piranha 8 (Area 3): Between the two flamethrowers on the rope.
Piranha 9 (Area 4): Under the lower Heat Seeking Missile Launcher, near the rope.
Piranha 10 (Area 4): Under the Wasp Nest, near the platform with the Ladder Spears on it.
Piranha 11 (Area 4): Between the 5th Chest and the rope to the right.
Piranha 12-16: If you've found all the Piranhas so far and got to the Hangmen's Arena, you're good to go, because the last 5 all reside in the Arena itself!
Note: The Piranhas found in the End Chest Room are purely for decoration.