You're thinking of The Horselord.
But, theoretically, any combat template should be able to take out a normal leviathan and the associated spawn, if they can stay alive (I.E. get HP faster than the water balls from the leviathan and normal krakens drop your HP). Hit area might do better for the spawn, though, until you get spawn numbers down.
I personally do white nets with a mage/mystic/weaver, in stone form, with a RC cast, and hitting the pile of spawn with a chain lightning when it first pops (having a water ele slayer Scrappers, I eliminate all the water eles with the first shot - then, it's a matter of getting everything left to target the RC long enough to take out the serpents and krakens).
Of course, you also have to be prepared, in case Scalis shows up (assumes tosser is High Seas enabled)