and now time for my predictions. Rebecca will win up till she engages somebody in a final 1 v 1 battle. this person begins to trash her. and then spits on her heritage. luffy, takes wind of this, and interrupts the fight out of rage. and then proceeds to fuck shit up (also giving away his identity. ) Rebecca takes luffy (who takes the mera mera fruit) out of the colleseum as a Riot begins. the two run away to the underground prison, where people are being turned into toys. where he meets up with his crew. then it's the strawhats vs Dressrosa's Gladiators, and Doffy's forces.
all of this could be wrong of course (hey, im not Oda) but i see no reason why not.