What it does
Expanding Force is a special Psychic-type move. In normal conditions it targets a single opponent — nothing special about it. Once Psychic Terrain is active on the field, everything changes: it becomes a spread move that hits both opposing Pokémon simultaneously, and it gains a 1.5× power multiplier on top of that. Both effects together make it one of the strongest spread coverage moves in doubles when the terrain is up.
The key mechanic: both the spread and the power boost are terrain-dependent. The moment Psychic Terrain ends, Expanding Force reverts to a plain single-target move. Everything about this move depends on maintaining the terrain.
Psychic Terrain is most reliably set by the ability Psychic Surge, which Indeedee brings automatically on entry. Terrain lasts five turns normally, extended to eight with Terrain Extender. Psychic Terrain also blocks priority moves against grounded Pokémon — a useful secondary benefit for your whole team.
Who runs it
Armarouge (37%): Base 125 Sp. Atk with Psychic-type STAB. Under terrain, Expanding Force coming off that Special Attack stat with the 1.5× boost and spread coverage hits extremely hard. Its bulk lets it survive a hit and still fire back.
Meowstic (39%): More of a support-leaning Pokémon, but Expanding Force gives it a real offensive option. Base 101 Sp. Atk isn't overwhelming, but terrain-boosted spread coverage threatens a wide range of targets without needing high raw power.
Hatterene (18%): Base 136 Sp. Atk — the highest offensive potential in this group. Terrain-boosted Expanding Force off that stat can produce staggering damage spread across both opponents. Hatterene is very slow, so it typically runs alongside Trick Room to move first.
Reuniclus (12%): Base 125 Sp. Atk, standard Trick Room team pick. Moves last under Trick Room, fires off terrain-boosted spread coverage in return.
Delphox (17%): Base 114 Sp. Atk, Psychic STAB. Solid terrain-based spread attacker, especially effective against teams with multiple targets that are weak to Psychic.
The core partner for all of these is Indeedee — Psychic Surge sets the terrain automatically, and Indeedee can support with Follow Me redirection while the above attackers fire off Expanding Force.
How to use it
The standard doubles lead is a terrain setter (usually Indeedee) paired with an Expanding Force attacker. Turn one you establish terrain and either immediately fire the spread move or use the first turn on control; turn two you cash the terrain-boosted Expanding Force into both opposing slots.
Spread move clarification: the terrain version of Expanding Force targets both opposing Pokémon, not all four. It doesn't hit your own Pokémon — unlike Earthquake or other full-field moves, no friendly fire risk.
Speed management matters. Hatterene and Reuniclus have very low base Speed, so they typically need Trick Room to move first. Armarouge and Meowstic have more workable Speed tiers and don't require reversed speed priority.
If the opponent has a terrain-setting ability like Electric Surge on a switch-in, or can use a terrain move, your Psychic Terrain gets overwritten and Expanding Force immediately drops back to single-target. Terrain Extender gives you more turns to work with, but terrain matchups are a real consideration during team preview.
Tips & strategy
Don't run this without a reliable terrain setter: Obvious in principle, but in practice it's easy to put Expanding Force on a Psychic attacker without locking in a stable terrain source. The ability-based setter (Indeedee) is the most reliable option because it's automatic and doesn't cost a turn.
Coverage blind spots: Ghost-types are immune to Psychic, and Dark-types resist it. If the opponent's lead or primary attacker is a Ghost or Dark type, Expanding Force's coverage value drops significantly. Build your team with answers to those matchups so you're not relying on a move that bounces off the front row.
Psychic Seed pairing: Any grounded Pokémon holding Psychic Seed gets +1 Sp. Def when Psychic Terrain is active. This triggers on the same terrain your Expanding Force needs, so you can double-dip the terrain resource — attacker fires the spread move, another teammate holds Psychic Seed for the defensive boost.
Terrain race awareness: Terrain abilities activate on switch-in and immediately overwrite the current terrain. If you've set Psychic Terrain and the opponent has a potential Electric Surge or Misty Surge lead waiting on the bench, they can wipe your terrain the moment they come in. Check field status before committing your key turn.