The ability to instantly split anything (and anyone) into many tiny pieces with just one touch. That would be an OP Emperor-worthy level power.
It may not work on the opponent with strong enough haki, but he could apply it to other things like their weapons, projectiles (i.e. bullets), long range attacks (like Zoro’s etc), on the ground they are standing on. He could destroy buildings or warship in an instant.
I don’t think Oda would ever give him such OP powers. Buggy would be too lazy to train his devil fruit to awaken it or to master it after awakening it (but who knows, the man always loves a good troll).
But if it happens, I like to imagine his awakened devil fruit powers to be like would be an extension of his ability to split his body into many parts, except that he would also be able to split his surrounding like Doflamingo or even people like Law (as long as they are not powerful Haki users like how Law can’t move Kaido’s body in his room).
In this scenario, I think the difference between Law’s and his is this: Law’s powers have more to do with spatial manipulation in his room. Cutting people up is just an effect of that.
One way I have thought of how Buggy would be genuinely OP if he could actually fight and use his awakened powers like: split a brick or something into really small pellets, then apply haki to them and fling them at his enemies. He could make anything into tiny bullets and just swarm people with them.
He also theoretically would be immune to swords considering how even Mihawk casually swinging at him didn’t hurt him. While Mihawk wasn’t trying at all, that’s still quite a feat.
Finally compared with my first idea, he also could be an absolute pain to fight since he could just separate himself out all over the place and then just leave hands together flying around punching you and splitting other things into projectiles.
Theory by Stingflare (https://www.reddit.com/user/Stingflare)