It's now March on my switch, ditto spawns are a nightmare.
Okay. So we all Know how Raids have a hp multiplier to make them harder to take down. (I.e a four star raid has 12x their normal health). My working theory is that when a Tera Raid Pokémon uses a move that's cuts a set amount of Hp, it cuts the base hp before the multiplier. (Ex. If a Pokemon has 100 hp, as a 4 star raid it has 1200 hp, but belly drum only takes 50 hp still.) Fillet Away also follows this rule. I haven't encountered a Ghost type ditto yet, but I'm willing to bet Curse will follow the same rule. Will update if I ever find one.
Explosion and Selfdestruct however, fail in Tera Raid Battles, regardless of whose using it.
Tldr, Moves that cut hp in Half only take small amounts of health instead while still providing all the bonuses, while self KO Moves aren't allowed in Tera Raids at all.
Update.
In the Most bizarre scenario, I found a Tera Type Ghost Flareon that knew Curse. It proceeded to do basically no damage to itself and curse my poor Houndoom. I believe this helps confirm my theory of Base Hp being used when Hp sacrificing moves are used.
Hope I helped.
