The regex for this (for left-facing creatures) is ^[aeimpvy][bcfgjknqtw]*[dhloruxz]$
Unfortunately, as you point out, all the vowels are in the end segments, so there's no creatures with a midbody longer than 2 letters. Here's what you get [0]:
ad ago ah and ankh awl ax ego eh end er etch ex id inch into itch
However, you can also include words that form multiple creatures [1]. Some favorites:
aggrandizer
alexander
equalizer
inlander
mumbler
phalanx
poacher
prelingual
voided
It actually gets a tiny bit better for upper case letters, as the midbody character set includes both U and Y. So the winner for longest single-creature word is: ADJUDGE
Unfortunately, as you point out, all the vowels are in the end segments, so there's no creatures with a midbody longer than 2 letters. Here's what you get [0]:
ad ago ah and ankh awl ax ego eh end er etch ex id inch into itch
However, you can also include words that form multiple creatures [1]. Some favorites:
aggrandizer alexander equalizer inlander mumbler phalanx poacher prelingual voided
0: https://regexdictionary.com/regex?r=%5E%5Baeimpvy%5D%5Bbcfgj...
1: https://regexdictionary.com/regex?r=%5E(%5Baeimpvy%5D%5Bbcfg...*