This would make sense... if they gave Sableye another three weaknesses (and yes Xerneas is OP but he can actually get hit). Without another weakness, GF would have to be insane to do that. The Wonder Guard ability is meant to be used on super-weak pokemon (not Sableye by the way) with multiple weaknesses. Why even consider this? Most likely, the gem is either a buffer, a free Substitute, or a defensive boost. Wonder Guard? Us Sableye fans (including me) wish
I'm thinking something more along the lines of Fur coat in that it boosts its defenses by 50% or something, which is still pretty damn OP if it gets a buff in its defenses. It's starting to worry me, I love Sableye. Sableye and Mawile are my favorite pokes from Gen 3, Mawile is all kinds of viable in OU, I don't want Sableye getting so buffed to where I can't use it in OU. :/