Cleon
Legend
For the attack lines, the original has a single unnamed attack that deals 6d6 points of damage.
If we go with the giant bite, then I'd say add imp grab and swallow whole (up to 1 size category smaller, even). Just seems to fit.
Giant bite, imp grab and swallow whole seems pretty good to me! Maybe they even curse those they swallow and spit them back out, just to add to the misery.
6d6 bite - ouch! I guess it's not surprising, as H4 is a notoriously high level adventure.
A single bite attack with all the trimmings works for me. How about it can distend its jaws to make a giant bite even when disguised as another creature, plus a multidimensional gizzard so it can swallow creatures larger than its external size would support. It could be "the old lady who swallowed a horse".
Drop summon tanar'ri since they are so loathed by their own kind? Or just give 'em a horrible chance of success?
I'd drop the Summon Tanar'ri altogether.