Water elementals are immune to acid damage.

The water elemental slams into its opponent or drowns it.

The water elemental gains a +10 bonus to hit points.

The creature is barely affected by weapon damage: metal bounces off it like a mere piece of wood, or the creature heals immediately. It gains damage reduction (DR) 5, subtracted from all damage it takes.

On an attack roll of 15-20, if the attack succeeds, the victim must succeed on a Strength or Dexterity check (its choice), DC [10 + the creature's Strength modifier], or be Knocked Prone. The creature reduces all weapon damage it takes (melee or ranged) by 2 (damage reduction 2). Spells deal normal damage.

The creature uses its great size to affect several creatures in front of it with a single blow. If multiple targets are in front of it, its attack affects two creatures (in a 180° arc). Make a single attack roll and compare it to each target's armor class. Its damage reduction increases to 4.