Here is the full list of all 50 FrightShow Fighter achievements.
Win 10 fights in a row
Win a round in under 10 seconds
Defeat a map without using Special Moves
Defeat StrangeWorld on Easy
Win 5 fights in a row
Defeat StrangeWorld on Medium
Win a round with <10% health left
Win 3 fights in a row
Perform a Special Move
Throw your opponent 10 times in 1 round
Win a round in under 30 seconds
Win a round in under 20 seconds
Jump 50 times in 1 round
Duck 50 times in 1 round
Fight the same character as you
Use a PowerUp
Play a local multiplayer match
Win 20 fights in a row
Win 50 fights in a row
Win a round by time out
Shoot 10 Eye Lasers in 1 fight
Launch 20 Ghosts in 1 fight
Throw 20 Canes in 1 fight
Summon 4 Cat Storms in 1 fight
Throw 20 Skulls in 1 fight
Throw 10 Chest Bombs in 1 fight
Throw 20 Bite Bears in 1 fight
Summon 20 Rainbow Dragons in 1 fight
Teleport 30 times in 1 fight
Throw 20 Boogers in 1 fight
Perform every possible basic move and attack in 1 fight
Win a fight by kicking only
Win a fight by punching only
Win a fight without getting hit
Win a fight with Special Moves only
Win a fight with every character
Lose a fight with every character
Lose a fight without landing a hit
Win a fight without missing a hit
Defeat a map without using PowerUps
Defeat a map with every character
Complete Story Mode 10 times
Defeat StrangeWorld on Hard
Defeat SpookyTown on Easy
Defeat SpookyTown on Medium
Defeat SpookyTown on Hard
Defeat DreadLand on Easy
Defeat DreadLand on Medium
Defeat DreadLand on Hard
Win a fight with Krunchy after losing Dr. Igg