Partially Used: Purple Worm

Maybe these guys should occaisionally have some really good loot? theyre not easy to kill with the whole stick + move thing and lots of hps... considering their unique attack form also would make sense that remains of other adventurers would be in there ripe for the picking.

Escaping gizzard with spells (even if they all require concentration checks) would be good to have as a possibility.

Agreed on both counts.

Perhaps casting a spell from inside the worm could even call for multiple concentration checks, such as one based on damage received that round and another just for trying to cast while being jostled by stomach muscles (though Stilled spells shouldn't be subject to the latter)

I forgot the loot? Oops. I got so busy trying to get the mechanics to work right that I missed the the undigestibles.