Abomasnow

Abomasnow has a great offensive typing, being able to threaten Water-types and top-tier threats such as Hydreigon, Mega Aerodactyl, and Crobat alike. While all these threats are faster than Abomasnow, it has a great priority move in Ice Shard, meaning it can pick off all of them fairly easily. Its typing gives it some nice resistances to Water, Ground, and Electric. It also can boost its Attack with Swords Dance quite easily, as it can force a lot of switches. Mega Abomasnow also gains a great Speed tier for Trick Room teams, as its abysmal base 30 Speed is one of the "fastest" Speed stats under Trick Room.

Unfortunately, Mega Abomasnow has one of the worst defensive typings, which gives it common weaknesses to Fire, Fighting, and Flying and undermines its nice 90 / 105 / 105 bulk. Mega Abomasnow loses Speed, which can be great for Trick Room teams, but it isn't that great otherwise, as a lot of common UU walls, such as Umbreon, Alomomola, Florges, and Tentacruel, outspeed and can proceed to get a free Wish off against Mega Abomasnow or threaten it with a Scald or STAB Sludge Bomb in Tentacruel's case.