Shadow Tag is one of those abilities that are viable in some situations and utterly useless in others. If Gothitelle comes in at the right moment, and tricks a Choice Scarf onto a Pokemon with a boosting move being used or a wall, Gothitelle is going to sweep. But, as the standard Gothitelle set only has Psychic moves, this makes a Gothitelle surprisingly easy to kill. For instance, no Dark Team should have any trouble with Gothitelle, as they cannot be damaged by Psychic/shock, and shake off the uncommon HP Fire. Any physical attacker that outspeeds Gothitelle (which will be pretty easy) that is able to OHKO Gothitelle should be good to go. Think Bisharp, Weavile, Hoopa-Unbound, Heracross, Dragonite, the list goes on and on.
Wobbuffet isn't really as bulky as one would like to think, however it is pretty hard to deal with if you are a mono attacker. Any Mixed Attacker has a fighting chance against wobbuffet.
Shadow Tag is definitely a dangerous force in the metagame, but it isn't nearly as unstoppable as you would think. Gothitelle Psychic Cores are really cool and can break many Mono Teams, as PK-Kaiser said.
Wobbuffet isn't really as bulky as one would like to think, however it is pretty hard to deal with if you are a mono attacker. Any Mixed Attacker has a fighting chance against wobbuffet.
Shadow Tag is definitely a dangerous force in the metagame, but it isn't nearly as unstoppable as you would think. Gothitelle Psychic Cores are really cool and can break many Mono Teams, as PK-Kaiser said.