Wait! I have an idea:
Meloetta @ Assault Vest
Hasty (+Spe, -Def)
252 Attack / 4 Special Attack / 252 Speed
Relic Song
Psychic / special coverage filler
Drain Punch
Knock Off
Sets up on Greninja, tanks hits, keeps itself healthy with Drain Punch. Relic Song has a 20% chance to induce sleep, and a fast sleep move that switches it back to bulky Aria forme might be handy.
It's a little gimmicky, but it might work. I've been experimenting with Assault Vest users as Greninja checks recently, and on paper, this sounds great. A fast, bulky Fighting type that can spam Drain Punch and Knock Off!
I'm probably being too optimistic, though...
