Day Twenty-five -- The Odobenus, a noble water elemental

Day Twenty-five of 30 Monsters in 30 Days. For those of you just jumping in, I'm using Matthew Finch's excellent "Tome of Adventure Design" to randomly generate a monster a day. I haven't quite hit my goal of one per day, but have kept things going, so that's good, I think.

Today the result is a 26, an elemental. It's nobility, similar to a powerful djinn. Mammalian in appearance, it originates from the plane of water. It can be bound through a sacrifice.  Hmm.

Odobenus
# Enc.: 1 (wilderness only)
Alignment: Chaotic
Movement: 180' (60') Swimming
AC: 4
HD: 8
Attacks: 2 (bite, tail) or special (see below)
Damage: 3d4, 2d6 or special
Save: F8
Morale: 12
Hoard Class: None
XP: 2060

Powerful, walrus-like elementals from the plane of water, Odobeni only appear on the Material Plane when summoned by a powerful magic-user; doing so requires a sacrifice of 20 HD of sapient beings, drowned in ocean brine. If the sacrifice pleased them (make a reaction roll, modified by +1 for every additional 20 HD sacrificed) they will serve the conjurer for a period of 13 days, although they primarily serve their own Chaotic agendas and may subtly twist orders to fit their desires.

Odobeni are only affected by magic and magical weapons. In addition to their powerful melee attacks, they may use the following special abilities, thrice per day:

1. Become invisible, as the spell.
2. Create an illusion, as per the spell Spectral Force.
3. Lower water, as per the spell, as a caster of level 16.
4. Cast Water Breathing, as the spell, on up to 8 targets.
5. Once per week they may control weather, as per the druid spell Control Weather, greater

Odobeni rarely leave the water, although they can survive both in and out of it, and when in the water suffer automatic half damage (save for 1/4) from fire-based attacks. Once per day they may create a whirlpool 120' in diameter and up to twice that in depth, capable of sinking all but the largest ocean-going vessels.