This Achievement/Trophy can be earned easiest through "Private Match
" & "Versus
You will want to select either "Swamp Thing
" or "Cyborg
" due to weaker characters will be to weak to pick the crocodile up. Weaken your enemy until they are about to be defeated then bring them over to the hanging crocodile and if you defeat them with the intractable object, you will unlock "Killer Croc
Here is a video guide incase you prefer them over written ones.