The Joker would be pretty damn dangerous if let loose in Marvel. He is really intelligent, not only like a chemist and inventor but as a tactical mind, even if most of his motives are chaotic his method are very well planned. He is also the deadliest non cosmical threat in DC Universe having dozen or even hundred confirmed one on one kills. During the Infinity Crisis he served the Royal Flush Gang all alone. He is a great fighter (Batman noting how unexpectedly fast he can be in multiple stories) feels little to no pain and his chaotic fighting style can get the drop from character less talented in close combat. He haves inmunity to poison and to mind reading (or a least resistance) and a uncanny skill to avoid death.
I can see him making Daredevil life living hell. And torturing most of the Heroes sent to fight him. Punisher would only get the drop on him if he caughts the Joker off-guard.