I accurately predicted Regieleki and Regidrago's stat spreads to a T when they were revealed, but never posted it anywhere so I never got to feel smug about it. This time I'm gonna post my predictions (and just says April Fools if I get everything wrong):

Friend Guard

Corrosion

Star Power (i.e. Huge Power)

Gonna jump on the Fairy Aura bandwagon, although after realizing Eternal Flower Floette's color palette is derived from Xerneas and Yveltal, I think they missed a huge opportunity to make her Fairy/Dark with an ability that combines both auras

Tough Claws

Aura Break

Drizzle

Either "Metallicize" or something specifically sound-related like Punk Rock/Liquid Voice

Sharpness

Defiant

Levitate

Bad Dreams, plus causes Dark Void to change into an attacking move like in PLZA

It launches its hands so as lame as it is, I'm gonna go with Long Reach

Psychic Surge

I think Klutz would be a funny way to give it functionally no ability while still being an improvement over Emergency Exit

Soul-Heart

Base Scovillain's design, stat spread, and Dex entries always made me think it should have some kind of gimmicky ability involving Physical & Special moves, like "all STAB moves function like Photon Geyser" or something in that vein

Toxic Debris

Gives a stat boost to non-Mega doubles partner

Thermal Exchange
No strong hunches one way or the other for the rest.