Shing

The one way I've thought of doing it without struggle would be sandstorm/hail chip damage with the abilities that set them. apparently focus sash isn't ignored like sturdy either, but I'm not sure if you can get one legit before that battle.

You can't get the Sash organically, unfortunately. Which is why they aren't used in successful takedowns, of course.

Even with weather damage, you will still end up yveltal using struggle because she has one full restore. Aka it will cover more than 10 turns. Well that tells yveltal's "signature move" just ignores the pokemons itself rather than the items. And no, I don't believe focus sash was ever implimented early in reju. And definetly not this verison. I try to check every items, and I haven't found a single sash yet.