Perospero said he wished he could have killed Marco many times in the past, so i imagine he has a good enough understanding of his abilities. Whatever he would do against him should take that into account, so my best guess would be the technique he used against Brook and Chopper, or a superior similar alternative
We also have this line from Marco
which makes me think that eventually, he will go directly after Kaido ?
So i could see a situation where he is turned into a Candy Man thing while the fights happen with King, Queen and Perospero, and after their defeat he's saved from that predictment, maybe by Perospero being taken out, and then he learns that the only remaining obstacle is Kaido, making him give his support to Luffy in the final stages of that battle.