If Lysandre Labs is in play and I use Primal Groudon's "Gaia Volcano" attack to discard the stadium and do enough damage for KO, what happens if the full HP Fighting-type Defending Pokemon has Focus Sash attached to it?

While Lysandre Labs is in play Focus Sash has no effect. However, Lysandre Labs is discarded as part of the attack before KO's are checked. So the Focus Sash would be in effect and if all of its conditions are met the Defending Pokemon is not KO'd but has 10HP remaining.

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