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