|Hellmouth, via Wikimedia|
The hellmouth does not have to be a potential campaign derailer. If you aren't ready to randomly throw some of the PC into a screaming torture-dimension, the hellmouth can suppress its throat-gate, allowing it to simply swallow folks into its flaming stomach. It is also designed to act as a living infernal siege engine, launching flaming boulders at distant targets and calling in reinforcements from Hell.
By the way, I've decided to start giving some adventure hooks below each monster, so even if you don't feel like reading a stat block, scroll down for dem sweet hooks.
The following text in gold is available as Open Game Content under the OGL. Open Game Content is ©2017 Jonah Bomgaars.