I just got it in a trade and it has a horrible moveset. It knows:
Muddy Water: STAB, good power, good chance to decrease accuracy.
Waterfall: Decent chance to cause flinching, good damage, high accuracy, STAB, makes use of Quagsire's higher Attack stat.
Water Pulse: Decent power, high accuracy, STAB, decent chance to confuse.
Water Gun: STAB, high accuracy.