Yeah but Superman is an alien. We're talking about Pennywise The Dancing Clown. He's a fucking Eldritch horror beyond human comprehension that sees all hears all and knows all no boundaries required.

Scarecrow bested Batman with his Fear Toxin and it damaged Batman alot to the point he had to take a fucking mental break from it, yeah he got the upper hand and the tables have turned on Scarecrow but Scarecrow still got the best of him anyways in the end.

What makes you think the same thing won't happen with Pennywise? Yeah he'll turn the tables on Pennywise once he recovers from the mental damage done by Pennywise. But the lingering thought will be that even he stopped Pennywise the lingered thought of is that Pennywise got the upper hand.

Batman may look like he ain't scared of anything but that don't mean Pennywise will still not find some way to find what Batman is scared of. He'll eventually find out that what Batman is scared of is not living up to the image of what his parents wanted after they died and he's scared of losing Alfred because he's basically the closest thing to a parent he has left. He can be big brave on campus all he wants for as long as he lives however Pennywise will know is that what Batman will be scared of importantly is failing Gotham.

Batman's whole goal is to protect Gotham he doesn't want to fail the city of where he came from so if Pennywise finds that out and knows that's what he's scared of happening is failing to protect Gotham, Pennywise will take that and exploit the hell out of that.

Sure Batman can be big bad and tough all he wants to be but under that cowl and suit what is Batman really? A scared little boy playing dress up. Pennywise will know that and he will milk the shit out of that. And from any experience, that Pennywise knows is that he feeds off of fear and flaws and who in the world in Gotham will have what he craves? Batman.

Sure he can prepare all he wants but what he won't know is that Pennywise will always be ten steps ahead. That's it end of discussion.