What it does
Insomnia prevents the holder from falling asleep. Any move that inflicts sleep — Spore, Sleep Powder, Hypnosis, Yawn — fails completely.
If the holder is already asleep when it gains Insomnia (for instance through an ability-swapping move), it wakes up immediately.
Know what Insomnia doesn't do: it only blocks sleep. Burn, paralysis, poison, freeze — all of these still affect an Insomnia holder. Confusion is not blocked. Fake Out is not blocked. It is sleep immunity, full stop.
Yawn specifically: it's sometimes treated as 'delayed sleep next turn,' but Insomnia blocks it entirely because Yawn's end result is sleep, and Insomnia doesn't allow sleep. No partial effect, no 'you're drowsy' — it just fails.
Who runs it
Ariados (93%) is the near-universal user. As a Poison/Bug type with modest stats, it's not a powerhouse, but Insomnia is a consistent tool against specific strategies.
Scovillain (0%) has access to it but effectively never runs it in practice.
How to use it
Insomnia's value is entirely against teams that rely on sleep as a strategy.
Spore and Sleep Powder are among the strongest status moves in competitive play — especially Spore at 100% accuracy. One sleep can lock a Pokémon out for two or more turns. An Insomnia holder ignores all of that and lets the opponent's entire setup fall flat.
Compare it to Lum Berry: the Lum Berry cures any status condition once and is done. It covers more ground — burn, paralysis, freeze too — but one use and it's gone. Insomnia is permanent but sleep-only and non-removable (unless by ability suppression). Against a team that's clearly built around sleep as its main win condition, Insomnia outlasts the Lum Berry over a longer game.
Tips & strategy
Insomnia is binary: if the opponent's game plan is Spore or Sleep Powder, it's a hard counter. If the opponent has no sleep moves, it gives zero value. There's no middle ground.
The choice between Insomnia and something else comes down to how often you expect sleep strategies in your bracket. At higher levels of play, Spore-based openers (Spore into setup) are real, and a dedicated sleep absorber has genuine matchup value.
One thing to keep in mind: an Insomnia holder can't use Rest to heal itself — Insomnia blocks all sleep, including self-inflicted. You cannot run the Hydration-style Rest loop on an Insomnia holder. The two abilities are mutually exclusive in that respect.