Though some state he has adapted certain beyond average endurances due to his original chemical submergence. The following are such noted enhancements:
Pain Resistance: It is speculated that the Joker's exposure to chemicals may have heightened his resistance to pain. It is also implied that he is masochistic in nature, and thus enjoys any pain received, making it an ineffective way of dealing with him.
Tainted Blood: Joker's blood is tainted. It has been said that "being an avid consumer of his products, Joker's immunity to poisons has been built up over years of dedicated abuse." When a mosquito sucks the Joker's blood, it "writhes and whines, choking on tainted blood".
Joker Venom Immunity: The Joker is immune to his venom.
Enhanced Intellect: Due to his chemical submergence.
The Joker has also shown other strange abilities:
Cheating Death: The Joker has cheated death numerous times, even in seemingly inescapable and lethal situations. He has been, among other things, caught in explosions, electrocuted, shot repeatedly (including point-blank in the face by a corrupt police officer masquerading as Batman), and dropped from great heights, but he always returns to once again wreak havoc.
"Comic Awareness": The Joker has, at times, shown to be fully aware of being a comic book character, even directly talking to the reader. However, most characters ignore this, due to the fact that he is criminally insane.
Inventive Skill: The Joker commits crimes with countless "comedic" weapons (such as razor-sharp playing cards, acid-spewing flowers, cyanide pies, and lethally electric joy buzzers) and Joker venom.
Genius-level Intellect: The Joker is also very skilled in the fields of chemistry, genetics, and nuclear engineering. He also seems capable of mastering whatever he puts his twisted mind to when he wants to. In a miniseries featuring the third Robin, he kidnaps a computer genius, claiming he is not too good with computers; however, later writers portray him as highly computer literate.
Skilled Combatant: Although he pales in comparison to any real fighter like those of the Batman Family, the Joker has frequently proven himself to be an excellent hand-to-hand combatant. While apparently of frail body, his ability to withstand seemingly any amount of pain, and the agility granted him by his insanity and willpower makes him a fearsome physical foe. He fights nearly completely unpredictably, and always has tricks up his sleeves for if he's losing. However, Batman and his allies often seem to be able to put him down with a single punch... but it is unclear whether or not he is simply allowing this to happen, as there are times where he is shown as being able to hold his own in hand-to-hand combat even against the Batman Family (including Batman himself).
Joker possess the strength level of an average human male who engages in regular moderate exercise though has at times due to adrenaline surges surpassed his normal levels; Athletic. However, he is mostly shown to be of weak physical strength.