Behir
Source: Monster Manual (2024) p. 34. Available in the SRD and the Free Rules (2024)

Behir
Lightning-Spewing Glutton
- Habitat. Underdark
- Treasure. Any
Twelve-legged, reptilian predators, behirs endlessly hunt for their next meal. Their short legs propel them quickly across floors and walls. Any prey that behirs can’t chase down, they blast with breaths of powerful lightning.
Legends claim the first behirs were magically created by storm giants during an ancient, multiversal conflict between giants and dragons. The giants used their mastery of weather to alter the essence of blue dragons. The results were the first behirs, which served as hunters with a particular taste for dragon eggs.
Behirs live in sprawling cave systems and elaborate ruins where they can make the most of their exceptional mobility. They are mindful of areas where dragons dwell, as most dragons view behirs as dangerous abominations and attack them on sight. Nevertheless, behirs occasionally hunt for dragon lairs in the hope of finding and devouring unhatched dragon eggs.
A quote from Lludd, Behir
You wouldn’t believe all the great stuff I’ve swallowed! Now just climb on in here, and you can keep whatever you find.