Static, but this ability is only used a few times such as Ash's battle with Ursaring.
Ash's Pikachu first uses his ability in Sinnoh, before that it is unknown if he has an ability.
Sources: watching the episodes and bulbapedia.
How to change your username
How to add a user avatar
Why was my post hidden?
Flags vs Downvotes
Official PokemonDb League
Type a Pokemon name, type, move or ability to see instant results.