The Joker is one of the most cunning criminals in the world. He is good at using long range, poking and deceive abilities to crack down enemies.
Abilities
Passive - Punch Line
After exiting battle, the Joker reloads his gun with enhanced bullets so that his next normal attack deals additional physical damage and increases attack range. The enhanced bullets also reduce target's movement speed and gradually weaken with its exceptional slowing effect. "Punch Line" can be used to assist your escape. So try to keep it for when it's needed.
Ability 1 - The Killing Joke
The Joker lights a cannon and launches a powerful rocket that deals physical damage to enemies in its path, but each subsequent enemy hit reduces its damage. This is the Joker's core ability. It's great for both clearing minion waves or safely harassing your opponent's. "The Killing Joke" requires a short period of charge time to cast. So be precise with enemy's positioning.
Ability 2 - Pick a Card, any card!
The joker removes movement speed and pairing effects from himself and gains movement speed as well as immunity to physical damage. Do not easily use the second ability. This can easily meltdown enemy's physical attacks even including more ads ultimate. But it cannot remove control effects and is vulnerable for magic attacks. Overall, all magic comes with a price.
Ultimate - Canned Laughter
The Joker rushes towards the target and ties a canister of laughing gas to them that stuns them for a short period. He cannot be targeted during the action. The canister then explodes dealing physical damage and reducing the targets movement speed.
The movement reduction effect gradually weakens over 1.5 seconds, and the Joker saunters back to his original position after the explosion. "Canned Laughter" is a directional cast ability that cannot be dodged. Its tremendous damage and speed make this one the better nukes in the game.
After the Joker finishes launching forward, he's immune to all control effects. Therefore, you could also use "Canned Laughter" as both an effective opener as well as an escape tool.
The Joker's common combo is to start with a passive enabled normal attack to deal massive damage and slow down the target. Then use "Canned Laughter" to rush to the enemy.
After the Joker jumps back, immediately release "The Killing Joke", then finally use the second ability to chase the enemy or escape to a safe area. A plus 1 plus A plus 3, according to progress of the battle.
This combo will give the Joker a perfect set of high damage attack in a short period of time. In the early game, the Joker can use "The Killing Joke" to clear minion waves and poke enemies.
Then, use the second ability to chase enemies down when they are running low. At the end, use normal attack or "The Killing Joke" to seal the kill.
In the mid and late game, the Joker should stay at the back of the team. Use "The Killing Joke" to deal damage when enemies are close. Release the ultimate to stun them and connect with "The Killing Joke" to nuke the target.
With the help of allies, this would allow the Joker to complete most of the kill and outnumber the opponents. But if it's not successful, immediately use deceptive magic to get out of the fight to prevent from getting focused down by enemies.
Lore
The Joker's origins are shrouded in mystery, but what is known is that he was once a small-time criminal who, after a freak accident transformed into the Clown Prince of Crime. The Joker's belief that life can change at any moment drives his thirst for chaos, which has fueled his reign of terror in Gotham City. Believing that life is nothing more than a cosmic joke, the Joker has dedicated himself to showing others- the whole world, even- that in one moment, your whole life can get turned upside down.
The Joker has kidnapped, crippled, maimed, murdered, and tortured countless individuals throughout the world, but his locus of operations is Gotham City. Or, it was. In Gotham, the Joker was obsessed with the punchline to his best joke: the destruction of Batman's ideals. Yet, try as he might, no matter how agonizing nor how elaborate the situation, Batman refused to give in to the Joker's games. Even after the Joker's actions cost Batman some of his dearest allies, the Dark Knight would not break. Instead, Batman turned the tables on the Joker by utilizing a highly modified version of Scarecrow's fear toxin.
Prior to this moment, the Joker had never truly tasted fear. With Batman's altered fear toxin sluicing through his veins, the Joker was terrified for the first time. the traumatic nature of the experience was enough to unmoor the last fastenings of the Joker's sanity. Rather than stand trial for his crimes, he was committed to Arkham Asylum. Here, the Joker was a comedian without a joke. What could be truly funny in the face of true terror? The Joker began to despair that he may never laugh at the world ever again.
That changed when a new inmate was brought into Arkham. This man, too, was mad, but in between his demented ravings he spouted lucid streams of mathematical equations and whispered incantations in hushed tones. And when he would sleep, a single phrase was on his lips: "Athanor….Athanor." The man's madness intrigued the Joker. With some charm and deception, Joker befriended the inmate and learned of where the man had come from. A scientist in a former life, the Arkham inmate had studied radiation spikes across the world that coincided with paranormal phenomena. The scientist had found the answer to these riddles: a portal to another world.
The scientist spoke of this realm, Athanor, with reverent tones. It was clear that the experience had changed the scientist profoundly. The Joker was not in search of spiritual enlightenment or an experience that would cure his madness; no, he longed to see this world of beauty and order, so that he might make a grand joke of it. With his mind finally resolved to a productive endeavor, the Joker escaped Arkham, as he had so many times before. This time, instead of wreaking havoc upon Gotham, the newly freed Joker made for Athanor.
After months of searching, the Joker finally found the portal to Athanor. And now, even the gods who content to rule that realm will have to wrestle with the man who is chaos personified.