[ADV] Offensive Cloyster

Cloyster (M) @ Leftovers
Trait: Shell Armor
EVs: 252 HP / 216 SAtk / 40 Spd
Rash Nature (+SAtk, -SDef)
- Ice Beam
- Surf
- Hidden Power [Grass]
- Explosion

It may seem unusual to you new-genners, but Cloyster in older gens is seen as a much more defensive poke, with its support moves in Spikes and Rapid Spin and significant enough offensive presence through Explosion and good STABs- in fact, its pretty much exclusively seen in a defensive role. This set is designed to take advantage of that mindset, alongside its good STAB combo and Explosion, and acting as a great offensive pivot and stallbreaker. Explosion is what really sets Cloyster apart from other special attackers, since it can take out the likes of Blissey, Regice and Snorlax with a little bit of prior damage (Gengar needs significantly more). Base 85 Sp. Atk may not seem like much, but with a +Nature and sufficient EVs, Cloysters STABs really do put a denting in those that don't resist them. HP Grass lets you beat non Thunderbolt/Psychic Starmie, and crushes Pert. HP Electric could work, but Rash STAB Ice Beam and physical bulk means you do well on Gyarados anyway.

Max HP gives you all the bulk you should need to switch in on physical hits like Swampert EQ, Mence HP Flying, or, if youre gutsy, Snorlax Body Slam. The Speed investment means you outspeed Claydol and anything slower, and the rest go in Sp. Atk so you can hit hard. Surprisingly hard. Rash is the nature of choice, since the only special attacks you want to be taking are Ice Beams and the odd Surf, and the Atk and Speed are too valuable to lose.