DeoGar teams are usually incredibly easy, except the one time I saw somebody with HP Fire on their Deoxys (that went downhill quickly), because Walrein absolutely loves HO teams which provide massive opportunities to set up. Usually I send out Forry first and just spin/Gyro Ball until they get bored and switch, and then play it from there.
Like I said in the post, the tough one is Jellicent/Ferro/Tentacruel on rain stall. Abomasnow beats all of them but can't switch in to hazards :P Usually I try to toxic jellicent and switch around between Blissey/Latias/Gliscor, none of whom mind hazards too much, although it is annoying. I do need a way to beat those teams. I think the quickest fix is Substitute>Psyshock on Latias because most of those teams can't stop +6 CM outside of Leech Seed/Toxic, but then I lose the only thing stopping CM Keldeo from destroying my team...so if anybody has any ideas, please let me know.