This is kind of inspired by an earlier post I did concerning a possible battle discussion concerning the Green Goblin going up against the World's Finest (which is saying, Batman and Superman at the same time):

https://www.fimfiction.net/group/199466/the-marvel-dc-co-fan-club/thread/520799/possible-battle-discussion-green-goblin-vs.-worlds-finest

In this case, Joker and Lex Luthor meet the Green Goblin when all three are in a super-high-security prison for captured super-villains awaiting trial. The Green Goblin observes that he has the Joker's insanity, plus Luthor's skills as both a scientist and a businessman plus actual superhuman physical abilities, which makes him more dangerous than both of them combined.

Joker points out that, if the Goblin is such a hotshot, why has he had so much trouble with Spider-Man?

Goblin comments that,

"WHEN the three of us can escape, we'll make a bet. You two BOTH take on Spider-Man at the same time while I take on YOUR two arch-enemies - Batman and Superman - by myself. They've had trouble enough with you two after all. And I'm a more dangerous hybrid of both of you.

If I can beat Batman and Superman on my own and you two both lose to Spider-Man, then I win the bet. If you two manage to beat Spider-Man while I lose to Batman and Superman, then you two win the bet. The loser or losers of the bet have to everything the winner or winners want for two months."

Of course, the three villains escape and make their preparations for the "enemy switch" bet - Joker and Lex Luthor against Spider-Man, Green Goblin against both Batman and Superman.

Of course, the Green Goblin is crazy, but not stupid, so he prepares a few weapons including Kryptonite, red sun light and some sonic stuff for messing with Superman's super-hearing. As for Batman, he already has the physical superiority advantage over him and very few easily exploitable weaknesses for Batman to zero in on.

And both Joker AND Luthor prepare weapons designed to exploit Spider-Man's weaknesses (which more bad guys don't do only because the majority of the villains in Spider-Man's rogues' gallery are already more powerful than he is anyway.)

And that is all I've been able to think of. Anybody who can think of stuff to add to this is very welcome to do so.