What it does
Eerie Impulse is an Electric-type status move that lowers the target's Special Attack by two stages. Two stages means the target's special output drops to roughly ×0.44 of the original — less than half. Most stat-lowering moves in one hit only drop one stage (roughly ×0.67). Eerie Impulse hits the two-stage threshold in a single action.
A special attacker that hits for a KO at full Special Attack suddenly can't threaten KOs after Eerie Impulse. That one move changes which matchups are comfortable and which aren't, without dealing any damage at all.
Ground-type Pokémon are fully immune — Electric moves don't hit them. Always check target typing before using.
Who runs it
Pikachu at 35% uses it as a field control layer alongside its own Electric offense. The combination of attacking and debuffing from the same slot pressure creates a difficult choice for the opponent: target the Electric attacker risking free damage, or let Eerie Impulse neuter their special attacker.
Dedenne at 20% uses it as a support dimension on an Electric/Fairy build — the same Pokémon carries offensive Fairy coverage and Special Attack debuffs.
Emolga at 9% pairs high Speed with Eerie Impulse. Acting before the target means the Special Attack drop applies before they fire their move — which is exactly when a pre-emptive debuff matters.
How to use it
In doubles, click it on the most threatening special attacker the moment they enter. The −2 Special Attack applies immediately, affecting every special move they fire from that point forward.
Ground-type immunity is the practical constraint. If one opposing Pokémon is Ground-type and the other isn't, target the non-Ground one without hesitation. If both are Ground-types, Eerie Impulse is useless — know this during team preview.
High-special-defense partners benefit most. A partner that was already tanking special hits comfortably now does so against a Pokémon hitting at less than half output — the stall potential compounds.
Tips & strategy
Eerie Impulse and Chilling Water are mirror images: one kills physical offense, one kills special offense. Read the opposing team's damage sources during preview and choose accordingly — or build a team that includes both for different matchups.
A fast user like Emolga clicking Eerie Impulse first means the special attacker's first move already comes in at −2. They don't get one free hit at full power — the debuff lands before they act.
Two-stage debuffs don't stack the same way as one-stage ones over multiple turns. A second Eerie Impulse on the same target drops them to −4 Special Attack, which is largely academic — at −2 they're already not threatening most things. Point the second action elsewhere.