I am homebrewing a monster that has incorporates the Swallow mechanic used by the Behir (MM, pg. 25). My monster is not at the same CR and I need to adjust its statistics accordingly, but there is one part of Swallow's text:
... the behir must succeed on a DC 14 Constitution saving throw at the end of that turn or regurgitate the creature.
How is the 14 DC calculated? Is there some formula to arrive at 14, as opposed to 17 or 12? Or is it less rigorous than that and more subjective?