[@WizardGirl] The toxin resistance is due to the chemicals that created him, as the Joker is immune to nearly every known toxin, usually more so than Ivy. 

He would simply know Ivy because of Harley, and probably knew her more when he was more sane, not after his break with the Joker.

And the cartoon logic thing is simply to state the way he moves,, pulls over sized things from his pockets, etc. 

He is essentially like the Joker in most aspects, just minor increases to his normal physiology due to the chemical bath that made him. He is, however less violent towards others than the Joker and proves to be very cooperative by comparison, hence why he was sent here.