Tera Shift
When Terapagos enters the battle, it turns into its Terastal Form until the end of the battle.
Full effect
When the Pokémon enters a battle, it absorbs the energy around itself and transforms into its Terastal Form.
In game description
When the Pokémon enters a battle, it absorbs the energy around itself and transforms into its Terastal Form.
Pokemon with Tera Shift
Using Tera Shift in Cobblemon
Abilities are passive and always active, so Tera Shift costs you nothing to run. If it is marked hidden on a species above, expect it to be harder to obtain: servers differ in whether hidden abilities come from breeding, an Ability Patch, or events.
See the Pokedex for which abilities each species can have, and IVs, EVs and breeding for how to actually pass one down.