In Regulation E VGC, when I used Bitter Malice (Which has a 100% chance on lowering attack) on a Rillaboom with Grassy Surge as it's ability, the attack drop did not happen. However, there was no pop-up informing me that it was holding a clear amulet, so for all I know it was not. The only other possible explanation is that it's partner was a Garganacl which could've had the clear body ability, also no pop up if this was what happened.
I do not have a link to the battle as the room expired while I was attempting to get answers, but I have managed to snag a download if needed