6 ways to use… behir

1) The behir, when on its own, is a hit-and-run enemy. Not because it doesn’t have the HP for a long battle (the more typical reason), but because once it’s swallowed an enemy, it has no reason to continue the battle.
2) Hit-and-run tactics provide a good way to get the PCs together into a narrow area (tunnel). The perfect setup for lightning breath.
3) When chased into a tunnel, the behir is smart enough to hide in a hole, (which can be in the walls or ceiling, thanks to spider climb) and then come out after the PCs passed and return the other way. This also lets it ambush the squishy back ranks, if it’s still hungry.
4) Beware chasing the behir onto ledges. It will instinctively avoid the weak spots, going back and forth between the wall and the ledge (via spider climb) so it doesn’t fall. The PCs will step onto a weak spot, and plummet down as the ledge breaks under them.
5) To shake things up more, place a tunnel behind a pile of rubble, or loose boulders. The behir will wait there to ambush the PCs, and will end up sending the stones falling onto them as it lunges out.
6) In a stalactite cave, the behir will move/jump from stalactite to stalactite for increased mobility. While it won’t step anywhere that will cause a collapse, the PC spellcasters might not be that careful, which will add falling columns to the battle.