Nyraala golems also have a second form; they can break down into mounds of seemingly inactive fungal growth. These mounds cannot move except to assume their golem form.
When an enemy is detected, nyraala golems reanimate their bodies in a gory implosion of mucous and flailing limbs, imposing a -3 penalty to their opponents' surprise rolls. Opponents who survive this first encounter may recognize the distinctive appearance of nyraala fungal mounds in the future (with an Intelligence check at a -2 penalty).
Two, nyraala golems can break their bodies down into a peculiar mound of fungal growth, providing them with a very effective form of camouflage. It is in this form that they are usually set to guard the dwellings and treasure chambers of their illithid masters.
This makes me think of mold wyrms. Think we can borrow some from their passive state?
We can use the Mold Wyrm's Camouflage write-up with a simple name-change, although we may want to modify the DC.Camouflage (Ex): Since a mold wyrm looks like a normal patch of fungus when in its passive state, it takes a DC 30 Spot check to notice it before it attacks. Anyone with ranks in Survival or Knowledge (nature) can use one of those skills instead of Spot to notice the plant.
Passive State (Su): When resting, mold wyrms spread into a 60-foot-diameter film of mold and fungus that covers floor, walls, and ceiling of its habitat. This fungal carpet always covers a cairn of obsidian rocks. Converting between its passive form and natural worm form (which uses the rocks as teeth) takes a full round.
Due to the trace of positive energy that holds the mold wyrm together, it heals at a rapid rate when resting. After four consecutive hours of rest, a mold wyrm heals any hit point or temporary ability damage that it had taken and returns to full health.
A mold wyrm must spend at least 8 out of every 24 hours in passive state. If it does not, it takes 3d8 points of damage each hour that it remains in worm form. If attacked, a mold wyrm always takes worm form, regardless of whether it has rested enough.
That's pretty good, but I don't know about the hour requirement per day or the rapid healing. That largely leaves the hangman golem version anyway. I'll go with the consensus on the healing, though.