Moves
Sludge Wave is the main STAB move, as it is very powerful and boosted by Adaptability. Sludge Bomb is also a viable alternative to Sludge Wave; however, while Sludge Bomb has a higher chance to inflict poison, it is often not worth using, because it cannot hit Chespin and might poison a Pokemon that would be crippled more by a burn. Hydro Pump, the most powerful STAB move on the set, is also boosted by Adaptability. Hidden Power Fire allows Skrelp to heavily damage Steel-types, which are immune to Poison-type moves; it is primarily used to KO Ferroseed, which resists both of Skrelp's STAB moves. Having Hidden Power Psychic allows Skrelp to OHKO Croagunk, which would otherwise counter Skrelp; it also hits other Skrelp for super effective damage. Scald is another 100% accurate STAB move, can be used when Hydro Pump's accuracy is not reliable, and has a 30% chance to burn the foe. Toxic Spikes can be used instead of Scald to provide chip damage that is useful for breaking Focus Sashes and Sturdy, wearing down walls, and putting a timer on opposing sweepers.
Set Details
The EV spread maximizes Skrelp's damage output while hitting Eviolite numbers. Adaptability boosts the power of Skrelp's STAB moves, and a Modest nature increases Skrelp's Special Attack. The Speed EVs allow Skrelp to outspeed Pokemon such as Spritzee and Hippopotas.
Usage Tips
Skrelp can easily switch into moves that it resists, thanks to its bulk. Scald should be used early-game to burn and wear down Skrelp's checks. Ferroseed and Croagunk should be hit on the switch, as they are not always OHKOed by any of Skrelp's moves.
Team Options
Sticky Web support lets Skrelp outspeed and KO Pokemon that would usually be faster than it. Hazard support can be useful to allow Skrelp to attain KOes more easily. Skrelp has good synergy with Fighting-types, such as Mienfoo and Timburr, as it can easily KO Fairy- and Poison-types, which are troublesome for them. Skrelp works well with Drilbur too, as Drilbur is immune to Electric-type moves, which Skrelp is weak to, can set Stealth Rock up, and can easily KO Croagunk, Skrelp's main counter. Pokemon that can deal with Abra, such as Stunky and Pawniard, are also good partners to Skrelp. Pokemon that are immune to Ground-type moves, such as Archen and Vullaby, and Pokemon that resist or are immune to Electric-type moves, such as Drilbur and Pumpkaboo, also make for good partners. Support Pokemon such as Spritzee, which has access to Wish and Aromatherapy, are also useful to allow Skrelp to stay healthy.