Some TMNT stuff really isn't for little kids.
After being injected with nanites, TV journalist Jack Ryder gained the ability to transform into the Creeper, a heroic psychopath who scares even the Joker.
Creeper appears only on the cover of Batman/Teenage Mutant Ninja Turtles #5, and does not feature in the story at all.
The Creeper that appears on the cover to Batman/TMNT #5 is clearly his Jack Ryder incarnation, but although insane, is not a villain. Furthermore, the current Creeper of the DC Universe (New 52) is an Oni, and would not be present at Arkham Asylum.