I am playing Cacturne PLF with Giant Plant Forest to get it turn one. No this isn't a speed variant, in fact, I don't need a speed engine to hit T1 Cacturne 95% of the time. I'll probably be the only one to play it, but who cares? We play Pokemon for fun right? I feel like no one agrees.
What I think will make top 4 is:
Giratina/Toad
Night March/Archeops
Vespiquen/Flareon
Yveltal/Archeops
Metal Rayquaza
Accelgor(maybe)
A couple of things. DON'T PLAY BLASTOISE. Yea, there's this card called Vespiquen, it will destroy you in your dreams. I went to an LC last weekend, and there was a ton of Vespiquen in masters and I might have been the only senior in top 4 who didn't play GiraToad, I played Night March. Besides the point, it has bad matchups in Night March, Vespiquen, and Toad.
As for Donphan, I know a lot of people have been hyping this card, but do you know why it became less popular at states? It's because 60% of decks became Seismitoad and it just couldn't handle it and Donphan fizzled out. Now, Toad still exists, and so does Archeops so don't get your hopes up too high.
Finally, I say maybe for Accelgor because there are too many ways around it(Virizion, Keldeo, Bunnelby) that I think it will have to hit a bunch of good matchups for it to do well.