What it does
Sludge Wave is a Poison-type Special spread move that strikes three adjacent positions — both opponents and your own partner. In doubles, spread moves deal 0.75x damage. There is also a chance to inflict Poison on any hit target, though this is not the move's primary draw.
Hitting your partner is the central constraint. Before using Sludge Wave, confirm your partner falls into one of these categories: immune to Poison via typing (Poison-type and Steel-type Pokémon cannot be poisoned), or has a role where taking spread damage this turn is acceptable. Partners of Grass or Fairy type take super-effective damage from Poison and will absorb full-power Sludge Wave hits — that's frequently not worth the trade.
Coverage: Poison hits Grass and Fairy types super-effectively. In a Champions environment where Fairy-type is prevalent, a Poison spread move can hit two Fairy targets simultaneously with a single action — that's the multiplier that justifies the partner-splash risk.
Who runs it
Glimmora (13% usage) is Poison/Rock, so its partner in typical compositions will often be Poison or Steel typed — both immune to poison. Glimmora's main offensive stat is Special Attack, so Sludge Wave's Special category fits naturally. It gives Glimmora two spread lines: Rock spread and Poison spread.
Greninja (16% usage) has high Special Attack and high Speed but doesn't get STAB on Poison moves. Sludge Wave here is pure coverage for Fairy/Grass matchups, filling a slot that its other moves (Hydro Pump, Dark Pulse) don't cover.
How to use it
The key question before using Sludge Wave in doubles is always: can my partner safely absorb being hit? If your partner is Poison or Steel-type, no problem. If your partner is Grass or Fairy, the spread damage hits them hard — usually not worth it unless both opponents are high-value targets that justify the trade.
The poison chance is bonus when it triggers. Stacked with other passive damage sources — weather chip, field hazards — it speeds up opponent HP erosion.
Tips & strategy
Spread moves deal 0.75x per target in doubles, but the trade-off is hitting two opponents with one action. Total pressure across the board is a key doubles concept — if you're chipping both opponents simultaneously, you're getting more done per turn than any single-target move would.
Poison-type immunity from Steel and Poison-type Pokémon means the poison chance never triggers on them, though damage still does (unless they resist Poison-type moves). Against an opponent board that's heavy on Poison or Steel types, Sludge Wave's secondary effect is completely dead — only the damage coverage remains. Check the opposing team's typings before leaning on it.
Feel free to use Sludge Wave when facing two Fairy-type opponents simultaneously — that's the move's best scenario by far.