i would assume gengar is pretty good in this tier, it rapes forretress trying to spin (especially with the non-existence of pursuit tyranitar / houndoom), the ground immunity is amazing, and it can explode on blissey/ho-oh to pave a sweep for something. sun boosted fire punch probably smacks the fuck out of metagross too.
This is definitely true. IMO, CB Gengar is a great gimmick set. CB Boom is obvious, Shadow Ball can actually 2hko the standard Lugia and hits the Lati's incredibly hard (can OHKO some set-ups), and you don't need any sp atk investment for sun-boosted Fire Punch to 2hko standard Metagross. If you're ballsy, Focus Punch is a guaranteed OHKO on Blissey with just one layer of Spikes down. Definitely relies a bit on the surprise factor, and is depending on winning a speed tie with the Lati twins (and with a theoretical max speed Lugia).
In lieu of the Lati's being so dominant, Knock Off can actually be useful even in it's low-power Gen 3 form, since it can get rid of Soul Dew. Deo-D is about the only viable user, though. I guess Bannette is there too.
Edit: Oh right, Sludge Bomb is also there as a stronger STAB option (hits Kyogre and Ho-Oh harder than Shadow Ball, hits Blissey pretty hard, can sometimes 2hko Blissey and Kyogre with spikes down), but that also invites Metagross and Groudon switches. Sludge Bomb is probably a better option than Focus Punch, but your main arsenal is going to be Shadow Ball, try to get a Fire Punch on a Steel if you can, then Boom as your going away present.