I'm thinking one with Water Absorb EV trained in Defense, HP, and Sp. Attack. I'm thinking for moves:
Surf: STAB, good power, high accuracy, double damage against foes using Dive, used to deal with Rock types.
Thunderbolt: Good power, high accuracy, chance to paralyze, deals with other Water types.
Ice Beam: STAB, chance to freeze, good power, high accuracy, type coverage, used to deal with Grass types.
Toxic: Inflicts toxic poison.
Lapras learnset