Swampert
Under rain Swampert becomes a problem: Swift Swim doubles its Speed so it outruns the field, and rain-boosted Waterfall/Liquidation plus Earthquake give near-perfect coverage. Its only weakness is a 4x Grass hit, and rain teams are built to remove or redirect that before it matters.
Don't try to out-click it in the rain with a slower attacker — Swift Swim means it moves first and the rain-boosted Water hurts more than you expect. Kill the weather, not the Swampert: without rain it's a slow 60-Speed mon you outrun and pressure freely.
Swampert is 4x weak to Grass. Giga Drain OHKOs most sets and heals Venusaur back up. Bring it in on the Swampert or its rain setter and the sweep stops cold.
Milotic takes rain-boosted Water hits comfortably (it resists Water) and Haze wipes any coverage that leaned on boosts. It doesn't OHKO back, but it stonewalls the sweep and buys turns to remove the rain.
Goodra resists Water and shrugs off rain-boosted Liquidation, and Sap Sipper means the rain team's Grass-checking Fake Out or coverage doesn't help them here. It pivots and pressures while your Grass answer lines up.
Swampert almost never brings its own rain — Pelipper (or another Drizzle setter) turns it on. The whole archetype folds if you remove the weather setter or bring your own weather, so treat the setter as the primary target, not Swampert.
Every answer on this card was checked against the live learnset and roster data shown above — a citation that no longer holds is dropped, not shown. Type-based answers are computed from base stats and STAB. Speed is the real level-50 maximum. This is deterministic and sourced — no guesses.