Shuckle can be used to some degree of success in UU but even in the lowest tiers Shuckle's terrible HP spoil its defenses... which are suppose to make up for a limited movepool and no offensive options whatsoever. Even its most viable sets are filled with filler moves... Toxic, Knock Off, Rest, etc.
And Power Trick + Trick Room + Substitute doesn't even work in UU. 3 turns to set up? (Send Shuckle out after TR, sub, then PT) There's a pretty considerable list of things that can break the sub while Shuckle is power tricking and then send the shelled worm flying with a single priority move. More importantly, this only leaves Shuckle with 2 attacking moves. Great, Stone Edge + Earthquake. There are things that, y'know, aren't weak to either of those.