Celebitwo
Celebi Clone
Ash will battle the LT in the Top 4. It's already confirmed that the Paul battle is the quarter final, the battle Ash lost in the last two leagues. And we already know he's gonna beat Paul, if you can believe the confirmed truth that he'll use Heracross's Sleep Talk on Darkrai.
So this means that Ash will for sure get to the Top 4 this time around, and if he'll win, which won't happen (as much as I'd love to see it), he'd make it to the finals.
How do you know that? Why cant the battle be in the final? Either way, how likely is it that Charizard will come back for the battle?
As for this guys other Pokemon, apparently there was a Heatran in the opening ceremony episode (but no Darkrai), reasonable to assume that this another one of his Pokemon.