Chaos Beast
This malevolent creature is a manifestation of the Chaos energy corrupting the world.
Appearance
The Chaos Beast has a chance of appearing at any time that you have max Chaos, eg 3. 
Combat
The Chaos Beast attacks moving member (and members in range), inflicting huge damage, as if being attacked by a creature several levels above the players.
In addition, the Chaos Beast will inflict random Effects or disease on every player.
The Chaos Beast use one roll in attack and have a huge chance of attack rolls.
Rarely, the Chaos Beast will attempt to use a single-target attack that rolls once, which has a possibility to fail its roll.
Scourge with random enemies change chaos beast into weak 0 level creatures, but only on land (possible bug?).
Trivia
If the Chaos Beast uses Steal it will attempt to flee the combat on the following turn. This is probably an unintentional effect of the Steal function, and is currently the case in Version 1.1.09. Even if the players defeat the Chaos Beast before it flees, stolen items will not be returned to them.