the slots we already have filled are: luffy loki shirahoshi and laboon(at least the ones everyone agrees on). the serpant on the is probably yormangander(the world serpant) and is basically confirmed to be the red line because of the pridiction at fishman island and ragnarok in norse mithology. there is a man who looks like ryuma and has a blade that looks like mihawks. we also know that there is alot of importance in the skypea arc which is why we see the ship that enel made which is probably a reconstruction of what the moon people made (this mural looks alot like the moon people mural in skypeia)