i wanna get a bit of discussion going about this thing because i think its really slept on in OU atm, and ive been experimenting with a couple of different sets.
1.) choice scarf. this thing is totally underrated atm, i think its one of the best scarfers in the tier. why? because its offensive typing is pretty much perfect for revenging the most prominent sweepers around atm: mega zard x, mega gyara, and mega ttar. all three are cleanly OHKOd by terrakions stabs, even at full hp. its also the only thing that can OHKO mega gyarados from full hp both before AND after it mevos if you predict right. on top of these, it outspeeds the most common scarfers in the tier, being garchomp, rotom, and excadrill, doing nice damage to all of them. if you can break the multiscale, you can revenge any dragonite also, because of the nice rock resist you can eat up extremespeed all day. it even outspeeds deoxys-s and has x-scissor for coverage, so if you can get deoxys to take some hazard and LO recoil damage, you can revenge it. if only this thing had u-turn > x-scissor it would be perfect :( scarf terrak fits very nicely onto HO teams as a get out of jail free card that means you dont have to sacrifice thundurus, and it also baits out and weakens stuff like skarmory and hippo, which is very useful if the team is built around a physical sweeper.
2.) choice band. on paper this set looks deadly, in practice it struggles to live up to expectations. banded CC has the raw power to OHKO alot of the metagame, even 2HKOing things on resisted hits, like zapdos and azumarill. the problem, however, is aegislash. this thing alone makes terraks stabs infinitely less spammable, and it makes using the set a precarious guessing game. will your opponent predict the CC and go into aegislash? or will they switch to their flying/levitating defogger, which 9/10 times resists CC? on top of this, will they protect to scout your move first, or switch directly? to use CB terrakion well in this meta you pretty much have to be a prediction god, and your opponent will always have something that can come in and force you out if youre locked into a ground move. specs keldeo pretty much does what CB terrakion does but better, because there are way less things that can switch into its stabs, and those that can have easily exploitable weaknesses (pursuit)
3.) swords dance life orb. i havent used this too much, but imo this is the way to go for using terrak on balance. no mindgames are needed, essentially. terrakion forces out alot of switches, and most peoples knee jerk reaction is to go out into aegislash. sucks for them, because +2 EQ is an OHKO and youre free to stone edge their flying/levitator after that too. like i say havent used this much yet but having used terrakion a bunch generally, i think its gonna be hot shit
so yea theres a few sets ive been using a bunch :)