What it does
Flash Cannon is a Steel-type special move with a chance to drop the target's Special Defense by one stage. The Sp. Def reduction is probabilistic but has elevated value in doubles — if it procs, your partner on the same side benefits immediately from the softer Special Defense, stacking pressure in the same turn.
Steel-type coverage reaches Ice, Rock, and Fairy targets while being resisted by Fire, Water, and Electric. In doubles, Fairy-type support Pokémon are consistently present, and Flash Cannon hits them super-effectively — making it a direct answer to the Fairy-type support archetype.
For Pokémon with strong Special Attack that also have Steel typing, Flash Cannon delivers STAB special damage without requiring any physical investment. Archaludon (Dragon/Steel) and Empoleon (Water/Steel) get same-type bonus on every hit.
Who runs it
Archaludon carries it at ~85% usage. High Special Attack plus Steel STAB makes Flash Cannon its most consistent damage output against Fairy and Ice targets. Its bulk lets it stay on field long enough to use it multiple times.
Empoleon uses it in Trick Room builds where its lower Speed becomes an advantage. Steel STAB, Fairy coverage, and the Sp. Def chance — all three properties are relevant.
Aegislash occasionally carries it for Steel special coverage alongside its form-switching strategy.
Lucario (Steel/Fighting) uses it for Steel STAB coverage against Fairy and Rock.
Hydreigon picks it situationally when Steel coverage is needed, though its primary damage usually comes from Dark or Dragon moves.
How to use it
In doubles, the first priority target is any Fairy-type Pokémon — Flash Cannon is super-effective, and Fairy-type support is common enough that this matchup comes up constantly.
When the Sp. Def drop triggers, the best-case play is having a second special attacker on your side to follow up immediately. A weakened Special Defense target takes more from both Pokémon. That's worth keeping in mind when positioning your two active Pokémon.
Under Trick Room, slow heavy-hitting Pokémon like Empoleon get to move first. A Flash Cannon that drops Sp. Def on turn 1 of Trick Room can set up a second attacker for a much cleaner follow-up hit.
Tips & strategy
Fairy-type Pokémon are the clearest trigger for using Flash Cannon over other coverage options — the super-effective hit is reliable, and the Sp. Def chance is bonus value on top.
Fire and Fighting types resist Steel, so Flash Cannon loses value against those targets. Know your coverage before the match and don't waste turns hitting resistant Pokémon when a better option is available.
The Sp. Def drop is an unreliable main plan. Build around the damage; treat the secondary effect as a bonus.