I'm pretty surprised that Scarf Gothitelle is under consideration, actually. It doesn't have that good attacking stats, and the best things about it are Shadow Tag and its SpD stat. That sort of calls for a SubCM set (which is what I'm currently using) or something similar to that. But a purely offensive Gothitelle doesn't seem as if it would be that good.
As far as trapped mons go, I've used it mainly against stalls (as far as August's list goes, I've set up on Cryogonal easily, but have not encountered the others with Gothitelle out). It's pretty good against Quagsire (thanks to Sub blocking Toxic) so long as said Quag doesn't carry Earthquake and have attack EVs.
However, Gothitelle almost always fails against an attacking mon. It's either 1HKO behind sub or else the other Pokemon usually wins (unless it's a special attacker, Gothitelle is CM'd up to the eyeballs and the other Pokemon does not have any SpA boosts). Practically any physically offensive mon is a counter. Spiritomb is pretty common nowadays, so it's yet another use for it. Dark types in general beat Gothitelle, another example being Absol, who also has Pursuit.
Another way I have used Gothitelle is by setting it up on the almost ubiquitous Uxie leads that currently plague the tier. Gothitelle can switch in on Uxie, sub, and then CM once before Uxie can do anything about it. If Uxie stays in (and doesn't predict the switch with Yawn) then Gochi can Shadow Ball, after all. (That's another question. Shadow Ball, Thunderbolt, they're all useful against Gothitelle counters. Good special coverage and only two moves to spare).
One last word: Psyshock. It's a better idea than Psychic, simply because it helps Gothitelle win "Calm Mind battles" with opposing Pokemon - taking advantage of the allied CM but ignoring the enemy CM. It's also useful against special walls that switch in expecting Gothitelle not to have a "physical" attack.
As far as trapped mons go, I've used it mainly against stalls (as far as August's list goes, I've set up on Cryogonal easily, but have not encountered the others with Gothitelle out). It's pretty good against Quagsire (thanks to Sub blocking Toxic) so long as said Quag doesn't carry Earthquake and have attack EVs.
However, Gothitelle almost always fails against an attacking mon. It's either 1HKO behind sub or else the other Pokemon usually wins (unless it's a special attacker, Gothitelle is CM'd up to the eyeballs and the other Pokemon does not have any SpA boosts). Practically any physically offensive mon is a counter. Spiritomb is pretty common nowadays, so it's yet another use for it. Dark types in general beat Gothitelle, another example being Absol, who also has Pursuit.
Another way I have used Gothitelle is by setting it up on the almost ubiquitous Uxie leads that currently plague the tier. Gothitelle can switch in on Uxie, sub, and then CM once before Uxie can do anything about it. If Uxie stays in (and doesn't predict the switch with Yawn) then Gochi can Shadow Ball, after all. (That's another question. Shadow Ball, Thunderbolt, they're all useful against Gothitelle counters. Good special coverage and only two moves to spare).
One last word: Psyshock. It's a better idea than Psychic, simply because it helps Gothitelle win "Calm Mind battles" with opposing Pokemon - taking advantage of the allied CM but ignoring the enemy CM. It's also useful against special walls that switch in expecting Gothitelle not to have a "physical" attack.