Well, in fairness, is “stiffen[ing] all the muscles in its body to raise its Defense stat” really any more ridiculous than all of the other stuff Butterfree can do? Whirlwind, Solarbeam, Dream Eater? Electroweb, for goodness’ sake? I mean, the fact that Butterfree can learn Electroweb surely implies that she can still produce silk of some kind, even though we don’t normally expect adult lepidopterans to do that. Gorebyss seems weird, but she actually has a higher physical defence score than Clamperl, so there isn’t really any reason Iron Defence should be inappropriate (especially since, on really any non-Steel-type, we should probably assume that it’s magic). And Gorebyss does in fact have shells; they’re just this… kinda weird… impractical bra thing. Actually harder to explain Huntail, but again, very high physical defence stat there. Maybe they both have calcareous scales or something. As for Shroomish and Focus Punch… well, this is why I normally refuse to deal with specific moves on specific Pokémon.