To add to the threat list (these are just some off the top of my head):
Offensive:
Haunter: Ghost / Poison. 115 base SpAtk, 95 base Speed. "Levitate". Shadow Ball, Thunderbolt, Energy Ball, Substitute, Explosion.
Marowak: Ground. 80 base Atk, 45 base Speed. "Rock Head". Thick Club item doubles this Pokemon's Attack stat. Swords Dance, Substitute, Earthquake, Stone Edge, Fire Punch, Double-Edge (recoil is canceled out by "Rock Head"), Boomerang.
Rampardos: Rock. 165 Atk, 58 Speed. "Mold Breaker". Swords Dance, Substitute, Head Smash, Stone Edge, Earthquake, Zen Headbutt, Endeavor, Fire Punch, Pursuit, Rock Polish.
Defensive:
Relicanth: Water / Rock. 100 base HP, 130 base Def, 65 base SpDef. Sleep Talk, Rest, Head Smash (recoil is canceled out by "Rock Head"), Aqua Tail, Waterfall, Earthquake.
Cloyster: Water / Ice. 50 base HP, 180 base Def, 45 base SpDef. Spikes, Toxic Spikes, Rapid Spin, Surf, Ice Beam, Avalance, Ice Shard, Payback, Explosion. "Shell Armor" blocks critical hits.
Slowking: Water / Psychic. 95 base HP, 80 base Def, 110 base SpDef. Nasty Plot, Surf, Ice Beam, Calm Mind, Grass Knot, Slack Off, Thunder Wave, Light Screen, Trick Room.
Articuno: Ice / Flying. 90 base HP, 100 base Def, 125 base SpDef. Substitute, Toxic, Roost, Ice Beam, Roar, Heal Bell, Rain Dance.
Muk: Poison. 105 base HP, 75 base Def, 100 base SpDef. Curse, Rest, Sleep Talk, Explosion, Gunk Shot / Poison Jab, Brick Break, Ice Punch, Payback, Focus Punch.
Gastrodon: Water / Ground. 111 base HP, 68 base Def, 82 base SpDef. "Sticky Hold." Curse, Stockpile, Recover, Surf, Ice Beam, Earthquake, Stone Edge, Toxic.
Other:
Lopunny: Normal. 65 base HP, 84 base Def, 96 base SpDef, 105 base Speed. "Klutz". Can Baton Pass Agility and Substitute. Switcheroo + Klutz, Magic Coat, Protect, Toxic, Encore, Toxic.
Piloswine: Ice / Ground. 100 base HP, 100 base Atk, 80 base Def, 60 base SpDef. Stealth Rock, Ice Shard, Avalanche, Earthquake, Stone Edge.
Venomoth: Bug / Poison. 70 base HP, 60 base Def, 75 base SpDef. Can Baton Pass Agility and Substitute. Sleep Powder, Stun Spore, Toxic Spikes, Roost, Screech, Bug Buzz, U-turn, Sludge Bomb, Psychic, Hidden Powers.