What it does
Simple Beam permanently replaces the target's ability with Simple. Simple doubles every stat change the target receives — Attack boosts, Speed drops, everything. That includes both positive and negative changes, so it cuts both ways.
The change is permanent for the match. Switching out does not restore the original ability. Only another ability-overwriting move can reset it. This is very different from a one-time stat drop — you're changing the game's rules for that Pokémon.
A few ability categories are immune: form-locking abilities like Multitype and Stance Change cannot be replaced. The move fails outright on those targets.
Who runs it
Audino at 73% is the dominant user of Simple Beam in this format. It runs the move as its primary disruption tool — Audino's own damage output is modest, so its impact comes entirely from support. Simple Beam lets it strip the functional core of ability-reliant Pokémon: a Storm Drain user that was redirecting your Water moves stops doing so the moment it gets hit. An Intimidate user that was cycling chip becomes a liability — your future Attack drops on it now count double.
How to use it
The most straightforward target is a redirector: Storm Drain, Lightning Rod, Follow Me — abilities that protect a partner by pulling moves away. Once Simple Beam lands, the redirect stops and you can aim at whichever target you actually want.
The more aggressive line is hitting your own teammate. If your partner is about to use Swords Dance, hit it with Simple Beam first. Now that +2 Attack becomes +4. Pair this with speed control — Tailwind or Trick Room — and you have a one-turn setup to a sweep threat.
The timing catch: Simple Beam has no priority. If the opponent switches on the turn you fire it, the move hits the incoming Pokémon instead. That might or might not be what you wanted. Against Pokémon locked into staying in — Trick Room setters, anything that needs to stay to accomplish a job — the hit is reliable.
Tips & strategy
The best targets for hitting opponents are functional Pokémon, not offensive ones. Stripping a redirector or an Intimidate looper is worth more than hitting a raw attacker, because the attacker's Simple will also double your offensive boosts onto them — it cuts both ways, and you might not want that.
For the ally-boost line, coordinate turn order. Use Fake Out on one opponent to freeze their response, then fire Simple Beam at your partner in the same turn while the partner uses their setup move. That way the double-boost kicks in immediately with no wasted turn.