Joker Psychology 101
The Joker is a character of malice, tricks, mischief, and lots of pain, due to his stippled past. He hides his true self from society because society has hurt him and people fear him because his jokes can be cruel, or worse. The Joker is compatible with similar jokesters, pranksters, clowns, and misfits, and he starts a Joker world with D.I.C.E. A Joker descends from primates and has features that let him commit tricks. All in all, the Joker can get along with people who are weird and funny like him, but normal people fear him.
The backstory of the Joker is sad and demented which gives him various Joker's tricks and perks. It is implied that the Joker lost members of his family and has no true home to return to. He claims to have killed his parents or brother in order to claim the title of Ultimate Joker, but we will never know if this is true because the Joker tells lies (nature of a Joker). His lies may be to protect himself and never face the truth of his sad life. Not only his past but his current life is pretty damn pathetic.
Jokers are compatible with other tricksters. This is why D.I.C.E. exists, and why he fell down those stairs. To a normal person, he is weird, and ostracized, so he puts on his theatre mask and plays up his jokes for shock value. When he sustained a head injury from slipping on a banana peel, the Joker pretended he died, but he actually had to go to the hospital, but no one liked him after that. The Joker also claims to kill people but he never directly killed anyone. It is unknown if the Joker is capable of killing people but the "prank" is that people think he killed people but he didn't kill anyone.
Some other noteworthy Joker facts is that he has opposable thumbs, meaning he can pick locks, break and enter, open containers, and use devices. Compared with other archetypes as the yandere, the hitman, and the water bearer, he has more dexterity, giving him ample opportunities to perform devious acts. When the Ultimate Pothead died, our Joker used his lockpicking to break and enter. He (The Joker) also has meagre knowledge of creating devices, and he enlists the help of Thomas Edison to invent a more evil Joker device.
Thus, our Joker has many qualities that let him perform acts of malice, but it is unknown if he is a threat to us. This is why we keep the Joker in a cage and monitor him 24 hours a day. If the Joker were to ever break out, he claims he will kill us all, but this is probably an "uso" (a lie). Because he is an usotsuki, we will never know the true nature of his capabilities, but his dextrous phalanges and prankster's heart makes him threatening to our cupboards and linens at the very least. Some people think that the Joker is delusional, and while he may have mental illness, most likely he protects the remaining purity of his soul with lies and simply enjoys a jokester's life.