If I have a Tera Pokemon on my Bench when I use Landorus' "Earthquake" attack, do they take 10 damage or not?
No, the Tera Trait protects them from damage by your own attacks as well.
Earthquake

Other known variants


x2
-20
Sleep PulseThe Defending Pokémon is now Asleep.


EarthquakeDoes 10 damage to each of your Benched Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)
If I have a Tera Pokemon on my Bench when I use Landorus' "Earthquake" attack, do they take 10 damage or not?
No, the Tera Trait protects them from damage by your own attacks as well.