Ability · Gen 9 · 1 Pokémon
Tera Shell
Terapagos: If full HP, attacks taken have 0.5× effectiveness unless naturally immune.
If this Pokemon is a Terapagos at full HP, the effectiveness of attacks against it is changed to 0.5 unless this Pokemon is immune to the move. Multi-hit moves retain the same effectiveness throughout the attack.
Tera Shell was introduced in Generation 9. 1 Pokémon and forms can have it.
Pokémon with Tera Shell
As a regular ability (1)
Terapagos-TerastalTera Shell FAQ
What does Tera Shell do?
If this Pokemon is a Terapagos at full HP, the effectiveness of attacks against it is changed to 0.5 unless this Pokemon is immune to the move. Multi-hit moves retain the same effectiveness throughout the attack.
Which Pokémon have Tera Shell?
1 Pokémon and forms can have Tera Shell: Terapagos-Terastal.
Effect text from Pokémon Showdown (MIT); which Pokémon have it from Showdown's Pokédex, cross-checked against PokéAPI. Unofficial fan site.