What it does
Shell Smash raises Attack, Special Attack, and Speed by 2 stages each, while dropping Defense and Special Defense by 1 stage each. Two stages of Speed means roughly double the Speed. Two stages of Attack and Special Attack means roughly double the offensive output. No other single move concentrates that much stat change.
The downside is real: −1 Defense and Special Defense means the user takes roughly 50% more damage than normal on the defensive end. After Shell Smash, one well-placed hit can KO the user. The implied contract is: smash and immediately sweep before taking any significant damage.
White Herb interaction: a held White Herb triggers automatically when any stat drops, restoring those drops once. Polteageist with White Herb uses Shell Smash, the −1 Defense and Special Defense get erased by the herb, and only the offensive and Speed boosts remain. That's the clean version of the setup.
Who runs it
Polteageist at 92% — the most concentrated usage rate in this entire group. Two paths: sweep directly after smashing, or use Baton Pass to pass all three +2 boosts to a bulkier partner. In doubles, the partner handles incoming attacks during the setup turn while Polteageist smashes.
Torterra at 52% is a physical sweeper that would otherwise be capped by low Speed. After Shell Smash, its Speed goes from slow to fast enough to outpace most of the field, and physical Attack becomes threatening.
Blastoise at 17% runs a Special set — post-smash Special Attack and Speed make it a water-type nuke with wide coverage.
How to use it
The setup turn is the vulnerability. Use it on the same turn a partner uses Follow Me or Protect, or on a turn you've forced the opponent into a poor position where they can't immediately KO the smasher.
After Shell Smash lands, attack immediately. Sitting on the boosts wastes a turn and gives the opponent time to Haze, Whirlwind, or land a hit while your Defense is lowered.
Tips & strategy
The Haze or Roar/Whirlwind hard-counter: any move that removes stat boosts or forces a switch erases the setup turn entirely. Keep the smasher alive until it can act, and be ready to absorb a redirect move if needed.
In doubles, Baton Pass is the safety valve — but without White Herb on the passer, the receiver inherits all stages including −1 Defense and −1 Special Defense. The White Herb on the passer is what prevents the defensive drops from transferring, not a mechanic of Baton Pass itself. Whether Polteageist holds White Herb determines whether the receiver is saddled with those drops.
Polteageist reversing from one of the slower Pokémon on the field to outpacing nearly everything is a psychological shift as much as a mechanical one. Opponents who planned to move first suddenly find themselves second.