The Punchroom is a mushroom-like creature that hops around in Fungal Forests. Although this mob has nothing to do with bugs, it is here to expand the mod from the "Insect Theme".
Punchrooms inflict only one heart of damage, but they do so with an insane amount of knockback, giving this "mutant 'shroom" its name.
They occasionally drop Elastic Fibre, and is the most constant source of the material if using Altars of Repair. Looting enchantments affect how many Elastic Fibres drop, and the chances of them dropping. With Looting III, you can collect up to 4 Elastic Fibres from one Punchroom.
Due to the knockback, it is ill-advised to fight Punchrooms unless you have a decent ranged weapon or until you're properly acquainted with life in the Erebus.