Leviathans

The Leviathan is probably one of the worst nightmares living on Mars. This huge worm waits under the surface until it feels prey coming by sensing the vibrations in the ground. It then will suddenly shoot out of the ground to attack with its many tentacles, before dragging the prey to its maw, to eat it. The only chance to win against this monster is to destroy the heavily armoured maw, as the tentacles simply re-grow.

Only well-equipped adventurer parties can survive this encounter and even worse, the Leviathan could appear anywhere on the surface of Mars.