All you need to stop a brain is a bullet.
"Alright where is the beast so that I can size it up?"
"That's the thing...you see that mountain range over there?"
"Yeah, the twin spires, what of it?"
"Well that's the beast"
"Bah, dere be no such thing as no 'peripheral beast'. How can their exist a creature you canno' even look at?"
Torax Shieldbreaker, Dwarven explorer
Rabbit-leonine like grass dwellers, for flavour
The PCs find a small green glass bottle, something can be seen writhing within the smoked glass. If the PCs open the bottle a repulsing form of life will pour forth and grow in size. A genderless beings of soft pliable purple flesh towers before the PCs, it has no detail, no distinguishing characteristics except for a narrow slit for a mouth that holds rows of inwardly curving teeth.