The mould (subspecies of fungus) is a playable race specific to Slash'EM Extended. They can be any role and alignment, and they start with uncurable polymorphitis and no way to acquire polymorph control or unchanging. Moulds are also unbreathing, mindless, lacking limbs and a head, and have difficulties picking up items from the ground while in their natural form.
A mould in their natural form has an increased chance of randomly polymorphing into something else. They can also stay in higher-level polymorph forms for a longer time before reverting back, and they can use the #youpoly command to change form at will (but without a way to choose what to polymorph into).
Their maximum stats are as follows:
A mould is severely crippled while not polymorphed; most actions that humans can perform, e.g. picking up an item from the ground or throwing a dagger, only have a 33% chance of success. Otherwise, the player is hit by a detrimental side effect that will make it even harder to do anything. However, polymorphitis has a chance of transforming the character into something that can actually fight monsters. Moulds don't experience the risk of "bad" polymorphs (system shock or polymorphing into a new version of oneself, which has the potential of instakilling a low-level character).
If you have enough mana, consider using #youpoly and hope to polymorph into something useful. A mould in their natural form will polymorph quite often though, so the player may just wait for the polymorph to happen.
Wearing a ring of polymorph control or an amulet of unchanging will not stop the mould from randomly polymorphing. Due to the difficulty of fighting anything while in mouldic form, this is probably a good thing.
A set of dragon scales or a dragon scale mail increases the likelihood to polymorph into a dragon without breaking the armor. However, even while polymorphed into a dragon, moulds can still randomly polymorph into something else, and if the new monster species is a nalfeshnee or other big monster, the player may break their dragon scales/scale mail.