Although Clamperl is slow and frail, she hits like a truck. When Trick Room is in effect, Clamperl becomes one of the fastest Pokemon in the game. Additionally, Her Water-typing gives her a resistance to many common priority moves, such as Ice Shard, Bullet Punch, and Aqua Jet, making her the ideal Trick Room abuser. DeepSeaTooth doubles Clamperl's Special Attack to an insane 542, turning her into a dangerous threat when used correctly. Surf provides reliable STAB, Ice Beam hits Grass-types, and Hidden Power Grass is for rival Water-types, like Quagsire and Milotic. Finally, Brine deals more damage to weakened opponents, which is especially helpful against Chansey and Registeel, while Toxic cripples defensive Pokemon who are difficult to get past. Keep in mind that when using Clamperl, it is very important that you switch her in unscathed, as her defenses are very low.
The idea behind this set is to be as slow as possible, so a Quiet nature and 0 Speed EVs are used. The IVs give Clamperl the lowest possible Speed while keeping Hidden Power Grass at 70 Base Power. Hidden Power Electric is an option instead of Hidden Power Grass, as it allows Clamperl to use a lower Speed IV of 2, though this leaves Clamperl vulnerable to Quagsire, Lanturn, and Gastrodon.
Clamperl appreciates the presence of entry hazards, as they greatly aid her sweep. Spikes and Stealth Rock are both capable of damaging the opposing Pokemon upon switching in, eliminating Focus Sashes and crippling bulkier Pokemon such as Registeel. Cloyster and Cacturne are wonderful choices to set up Spikes, while Registeel and Donphan are good choices for Stealth Rock. Toxic Spikes are also awesome, as they cripple bulky Water-types like Milotic and Slowking, though they also activate Guts, which is the main downside to using them. Omastar and Nidoqueen both do a good job at setting up Toxic Spikes due to their high defensive stats.
Trick Room support is vital to Clamperl's success, making Uxie, Claydol, and Solrock good partners. Claydol and Solrock are probably the best, as they can set up Stealth Rock and then Explode after setting up Trick Room, allowing Clamperl to switch in unharmed. Rain Dance support is also helpful, boosting the power of Clamperl's Surf. This can be set up by Pokemon such as Uxie, Slowbro, and Mesprit.