Powers:

The Joker has no super human powers however, he is proficient in hand-to-hand combat and is skilled in the use of firearms.

Weapons: The Joker often employs weapons or equipment created with a joke theme. He is usually armed with a handgun.

Joker Venom: The Joker often employs a poison that is almost always fatal when administered. The victim is left with a Joker like smile on their face.

Origins:

The Joker’s origins’ are shrouded in mystery. From his own fractured mind comes the tale of a man, a failed comedian whose wife and child were killed in an accident. He was conned into helping some criminals rob a chemical factory. The robbery went wrong and to escape he threw himself into a vat of chemicals. Eventually he washed up on a shore his skin bleached chalk white, his hair dyed green and his face stretched into a terrifying grin. The shock of seeing himself pushed him over the edge and he became the clown prince of crime the Joker.

Notes:

The Joker is a mass murderer with an unknown body count; significantly he has murdered Jason Todd the second Robin and Sarah Essen Gordon the wife of Commissioner Gordon.

The Joker paralysed the original Batgirl Barbara Gordon, by shooting her through the spine.

The Joker at Batman Wiki

The Joker at DC Database

The Joker at Comic Vine