>Hidden Abilities change each new generation. That means they won't rollover, so Contrary Serperior is dead on arrival.

>Pokemon that previously only had 1 ability and 0 HAs now have a HA assigned to them. So Mew gains Protean and keeps Synchronize because Synchronize was already a regular ability.

>Mega Pokemon also get their ability replaced with a new one. Mega Alakazam loses Trace and gains Pure Power.

>Primals are unaffected. So is Arceus.

Bulbasaur family: Dry Skin
Mega Venusaur: Aroma Veil
Pikachu family: Victory Star
Eevee: Protean
Espeon: Tinted Lens
Umbreon: Filter
Vaporeon: Dry Skin
Jolteon: Iron Barbs
Flareon: Fur Coat
Leafeon: Natural Cure
Glaceon: Refrigerate
Sylveon: Serene Grace

Gen 7 meta more cancerous than gen 6? Or this is bullshit?

Source:

http://www.smogon.com/forums/threads/new-hidden-abilities-discovered-code-underway-for-hidden-ou.3527099/