Marshtomp

Mud Shot + Surf and Mud Bomb

The most straightforward moveset available to Marshtomp, with an emphasis on its two STAB charge moves backed by the one of the highest energy-generating fast moves in the game. Combine extremely quick energy from Mud Shot with two STAB charge moves that only cost 40 energy each, and Marshtomp quickly gained a reputation as a speedy charge move spammer. Even though Surf (1.63 DPE) and Mud Bomb (1.38 DPE) don't pack as much of a punch as other charge moves, the damage does stack up rather quickly if unshielded. 

Mud Shot + Surf and Sludge

This moveset is just as quick as the previous one, but drops Mud Bomb for coverage against Marshtomp's only weakness: Grass-type Pokemon. From a stats perspective Sludge (1.25 DPE) is actually a very poor move, but a low energy cost (40) mirroring Marshtomp's other charge moves makes it easy to use and doesn't require shield baiting. There's also the extra perk of bruising the popular Azumaril pick. As a side note, swapping for Mud Bomb instead of Surf isn't as advisable due to the latter's higher damage, but can still work depending on the matchups.