Swamp Horror

A Swamp Horror is an Undead mist wraith that is encountered during the Baldur's Gate II: Throne of Bhaal campaign in the Forest of Mir – The Temple area.
A group of mist creatures are produced during a cut scene with Gorion, or an entity appearing to be him. This strange sequence results in a hostile encounter for the party.
They are immune to weapons less than +2 enchantment. They have complete immunity to acid, cold (including magical cold) and poison damage, and 50% Magic resistance.
The creature has a rapid Regeneration ability - 2 hit points per second (12 per round).
Note the creature's immunities and special abilities listed on the InfoBox.
A Swamp Horror's tendril-like melee attack weapon inflicts a 2d8 Crushing or Slashing (selected by the AI regarding the most favorable THAC0 value on the target). Additionally, 1d8 Cold damage is applied. The cold damage is the elemental type and is unaffected by magic resistance or Power level spell protections.
Each successful weapon strike on a target has a 30% probability to cause a Panic effect as well as a -10 Morale modifier reduction, with a duration of 5 rounds. A Saving throw vs. spell with a -2 penalty will negate these effects. Magic resistance can block these, but Power level spell protections will not.