What it does
Sandstorm shifts the weather for 5 turns. Non-Ground, non-Rock, non-Steel Pokémon take 1/16 max HP at the end of every turn they're on the field. Every Rock-type Pokémon gets a 50% boost to its base Special Defense for as long as sandstorm is active — no extra setup required, it fires the moment you set the weather.
Two side effects worth knowing: Solar Beam and Solar Blade lose half their power, and recovery moves like Moonlight, Morning Sun, and Synthesis only restore 1/4 HP instead of 2/3. Carry Smooth Rock to push the duration to 8 turns.
Who runs it
Stunfisk is the Champion-format sandstorm setter at 13% usage — a niche but deliberate slot. Its Ground/Steel typing means it takes zero chip from its own weather, and Steel neutralizes its potential Poison weakness. Running Sandstorm on Stunfisk is about enabling Rock-type partners defensively, not about raw damage.
How to use it
Sandstorm does its best work as sustained background pressure. Two specific situations: when the opponent is relying on passive recovery (Moonlight dropping from 2/3 to 1/4 HP is a huge nerf to stall strategies), and when you have a Rock-type defensive core that wants the SpDef boost to survive special hits it normally couldn't.
The chip is 1/16 per turn, which sounds small, but over 5-8 turns against 1-2 Pokémon it adds up to real damage without you spending any move slots on attacks. Against fast-paced doubles teams that don't have a Rock/Ground/Steel pivot, every turn in sandstorm is free chip.
Tips & strategy
Sandstorm loses weather wars to rain and sun — the last weather set wins. If your opponent runs Drizzle or Drought, your sandstorm evaporates the moment they lead with their weather setter. Check opponent team preview carefully before committing the Sandstorm turn.
The Rock SpDef bonus is the real reason to run this over other weather options. A Rock-type partner that would normally fold to a special attacker can suddenly tank a hit and respond — that's a tempo swing that can decide a game. The 13% usage reflects that sandstorm is format-specific tech, not a general-purpose pick.