Board Thread:General Discussion/@comment-76.28.110.96-20130511212536/@comment-9974415-20130608012107

FX8 wrote:
 * TMNT - mutated turtles
 * Splinter - bit by rat
 * Snakeweed - mutated in weed garden
 * Spider Bytez - mutated with spider
 * Pete - mutated pigeon
 * Dogpound - bit by Shredders dog
 * Fishface - touches fish
 * Leatherhead - mutated crocodile
 * Justin - mix of animal DNA in mutatgen
 * Chong - mutated cockroach
 * Pulverizer - they wouldn't want a 5th turtle so the creators turned him into a pile of organs in goop.

The reason Pulverizer turned into a pile of organs and goop was because he didn't come in contact with an animal before being mutated, so it just turned him into the next best thing... a blob.