What it does
Sand Rush does two things in sandstorm: doubles the holder's Speed, and makes it immune to sandstorm's residual damage. Both parts matter — without the immunity, you'd be eating 1/16 HP per turn while relying on the boost to sweep.
The Speed numbers are the story. Excadrill runs base 88 Speed, which becomes an effective 176 in sand — with full Speed EVs that's roughly 198 effective, faster than most uninvested or lightly-invested mid-speed threats. Lycanroc at base 112 hits 224 in sand, which clears nearly every non-boosted Pokémon on the field. You're not winning a Speed tie in sand; you're ending it before it starts.
This is a weather-dependent ability. No sand, no boost. The entire team needs to be built around that condition.
Who runs it
Excadrill uses Sand Rush at 85% and is the archetype sand sweeper. Ground/Steel typing with Earthquake and Iron Head gives it clean STAB coverage across a huge chunk of the format. Its job is simple: partner sets sand, Excadrill comes in at 176+ effective Speed and starts clicking Earthquake.
Lycanroc runs it at 95%. Rock typing with Stone Edge as the main nuke, and critically, Accelerock — a +1 priority Rock move. Even when sand gets replaced, Accelerock still fires first. That backup priority makes Lycanroc less all-in than it looks. At 224 effective Speed in sand, it outspeeds almost everything and can click Stone Edge freely.
Both need a sand setter in the team — Tyranitar or Hippowdon are the usual options.
How to use it
The sequence is: sand setter leads and establishes weather, then you switch Excadrill or Lycanroc in on a favorable turn to activate the boost. The Speed doubles immediately, so that same turn you're already faster.
In doubles, Excadrill next to a Fake Out user is a classic opener — Fake Out pins one opponent, Excadrill runs over the other. In singles, Lycanroc's 224 Speed lets it threaten sweeps with little setup.
Weather control is everything here. If the opponent has their own weather ability — Drizzle, Drought, Snow Warning — whichever weather setter moves last controls the field. If you lose the weather, you lose the Speed.
Tips & strategy
Earthquake from a Pokémon moving at 176+ effective Speed hits both opponents in doubles before most of them can respond. Your partner must be immune to Ground — Flying type, Levitate, or Air Balloon — otherwise Excadrill chips your own team.
Accelerock's priority is Lycanroc's safety net. When the sand drops, it falls from 224 Speed to a much more manageable 112. But +1 priority ignores Speed entirely, so Accelerock still fires first and can clean up weakened targets or revenge kill threats that outspeed it in neutral weather.
Sand Rush gives zero Speed bonus in rain, sun, or snow. If the weather shifts mid-game, the boost vanishes instantly. That's not a recoverable situation unless your sand setter can immediately restore it.