The Joker stole Darkseid's powers but he couldn't control them so he ended up using up all of the power by opening a big wormhole to another dimension. He managed to bring flash grenades, handguns, a bottle of Joker Juice, his acid-squirting flower, and some of his laughing gas to the other dimension. He arrived in the middle of a huge battle. Spider-Man had teamed up with Venom to take on the Green Goblin and Carnage. Spider-Man's battle with The Green Goblin had been taken outside, and Venom was battling Carnage inside. No one seemed to notice the Joker. Carnage punched Venom onto the ground. The Joker ran over to Venom.
Joker: "You look like you could use a little laugh!"
He poured the whole bottle on Venom. Most of it sank into the Symbiote, but some got through to Eddie Brock. Eddie began laughing uncontrollably until he died. The Symbiote slithered off... and possesed the Joker.
Carnage: "What the hel-"
WHAM!!!! Joker/Venom punched Carnage through a wall. Suddenly, the Green Goblin flew in on his glider holding Spider-Man's corpse.
Green Goblin: "Hey, Cassady, I killed the spider- wait, what the hell?!"
Now, this is an interesting part. As I mentioned Earlier, the Joker Juice sank into the Symbiote. Well, because of this, the Symbiote's webbing became spiked with the Joker Juice. So when the Symbiote hit someone with its webbing, that someone would die of laughter. And this is excactly what happened to the Green Goblin. The Green Goblin fell off his glider laughing. Eventually the Green Goblin stopped twitching and died.
The Joker/Venom: "Heh. Four people dead. Not bad in a day's work."
Carnage smashed through the wall.
Carnage: "Ok, NOW I'M ANGRY!"
Joker/Venom: "Meh. Well, It will be four people dead soon..."
They charged at each other.
So its Joker with the Venom Symbiote on him vs. Normal Carnage. Joker/Venom's Toxic webbing won't work on Carnage because Carnage is a Symbiote. Because the Symbiote is now on a more powerful host, it can now move as fast as Carnage and lift as much as Carnage.