Ascomoid

This misshapen sphere of pale yellow-green fungus rolls with an unnerving speed, spewing clouds of foul spores as it advances.


Source: Pathfinder Bestiary 3

     The Ascomoid is a large ball of fungus with fearsome mobility. Rolling around in their dark damp caverns the Ascomoid is capable of trampling their prey. Once a victim is crushed to death their bodies become host to a colony of fungi. Over the course of 48 hours the body is covered in brown-green mold. Within a month a new Ascomoid is born.
     The tunnels of Ascomoid is littered with the bones of it's prey. If the cavern has enough moisture it can support the life of a deadly cluster of 2 to 8 of these creatures. Some underdark races lead their enemies to the tunnels systems of the Ascomoid. The slightest vibrations triggers their tremorsense and the corridors quickly become death traps.

Combat; The Ascomoid is a large plant and has a challenge rating of 5. The special attacks of the Ascomoid is the ability to trample an opponent. By using its trample ability it simply needs to roll over a creature who occupies a space. The enemy can take an attack of opportunity or attempt a reflex save for half damage. 

     The Ascomoid can also shoot a jet of deadly spores. The spores fill a 10ft radius spread. Those who fail a fortitude saving throw become nauseated. Also the cloud exposes them to poison that the spores carry. The inhaled poison damages one's strength over time. With one shot of spores it requires the PCs to make two fort saving throws. 

Verdict: I have actually used a Ascomoid before. I was running the Darkmoon Vale modules for 3.5 and created a side dungeon for the group to explore. While underground they had to cross a long bridge over a very deep chasm. As they were halfway across the bridge an Ascomoid came rolling along. The bridge was only 10ft wide. Panic ensued among the group with some PCs hanging from the side of the bridge before the encounter was over. Luckily no one died but it was a very fun encounter.