Joker asks why so serious to someone.

And Sirius, just apparating there, gets offended, and stuns the joker.

Thus starts an epic prank war btw joker and the lieutenant of the marauders.

Joker gets irritated that the prank war is on hold due to wizarding war 2. He helps the order decimate the death eaters. Since he is so good at it. Sirius, knowing joker will burn the money, pays him off with Leprechaun galleons, which blasts when burning and colours the joker gold for months. ? ﾟﾘﾂ

And so goes the prank war.

Joker starts getting help from other villians, and sirius, with a bang, brings in the twins.

Literally, with a bang.

Batman's headache increases! Though there's no crime rate ? ﾟﾘﾂ He knows how it feels like 'people disappearing once finish taking with you' done to him often.

After Gordon speaks to forge(what a weird name for a shopkeeper) and tells how he contacts batman, and how he is there one moment and the next, he is not.

Batman searches all the likely places the twins can disappear to, without considering magic ? ﾟﾘﾂ

Also, the twins successfully maintains like forge and gred are two personalities is the same person, and so have alibis every single freaking time...

And they always prank batman and joker at the same time.

One always thinks the other is lying! ? ﾟﾘﾂ

Prank underlying a prank.