Leviathan would need something that competes with Contagion but does not overpower it.

Just for fun:

TAIL WHIP: deals x damage to target. Creates a small wave from the target that deals x (smaller value) damage to surrounding targets.

UNDERTOW: draws enemies within x range of target together and inflicts Heavy for x seconds. This would allow for easier use of AoE.

DROWN: Deals x damage over time and lowers enemy Strength. Just another DoT, since we are a DoT job.

EROSION: Applies a DoT for x seconds with potency that increases based on the number of active DoT effects. This would be like Fester, but a DoT rather than a direct hit, and would include the effect of Drown.

TIDAL WAVE: Deals AoE damage. Leaves behind a ground effect that continues to deal damage.