There are many legends about creatures and spirits which haunt sweat tents, saunas and bathhouses. In Russia, a creature known as the Bannik dwells within the Banya bathhouses, whose job it is to punish those which cross into its domain and break its laws.
They reveal themselves only when unhappy with the bath or if someone had been disrespectful. If Bannik becomes angry, watch out! Bathers were known to have lost their skin and had their bodies wrapped around the stove for loud singing, talking or swearing in the bath--or simply for being a stranger. You are wise not to lie or boast, and certainly not to have sexual intercourse in the bath! There are traditions that appease Banniks, including the drawing of a cross over one's shoulders, and altars of birch, lye or salt.
Bannik spirits appear as floating charcoal blobs with vaguely human form with any shape of limb forming and melting constantly from its body. Cracks and splits in its hide reveal molten lava or red plasma underneath. From within its body emits either groans of pain from a furnace of heat from the hole where its mouth should be or the angry sounds of hissing and bubbling, including a subsonic vibration that is 'felt' more than heard by those nearby.
Unlike the Jann, bullets aimed at a bannik will hit solid substance, but they splash into the magma form and ricochet sparks off its black body then stick like a dart for a moment before melting altogether. Bladed weapons are likewise useless against a hot bannik, which slashes open its plasma-like body, leaving gashes that quickly reseal behind.
A Bannik can injure and attack in horrible ways. In an encounter seen in Dealing with Devils, the Bannik hung up a victim and flayed it alive. A particularly gruesome punishment for the cannibal misusing its domain, because they usually smother humans like someone caught in lava flow.
The only way to kill them is essentially to freeze them solid. Industrial coolants, liquid nitrogen, and ice-cold water and the like. Once blasted, the bannik solidifies enough that a solid enough blow to remove its head will shatter its body and leave smoldering blobs of charcoal behind.