Thanks for this adventure! It was fun to run for my players. We played in-person and I made Ryle out of real chocolate, marshmallows, and licorice (and toothpicks). He started melting during the battle which actually worked out nicely. The player with the killing blow got to eat him!
I made some legendary/lair actions for Ryle, since my party had six people and can really mow through the hit points. I'm including my actions in case that's useful for anyone else.
Legendary Action: Coming Back Up
Ryle points a finger at a target he can see. The contents of their stomach instantly decay in a blast of gas and rot. The target must make an Constitution saving throw DC 16 or take 7 (2d6) poison damage. Ryle regains hit points equal to the damage taken.
Legendary Action: Wild Swings
Ryle makes two slam attacks, each attack is made with disadvantage.
Legendary Action: Chocolate Surge
Ryle moves up to half his speed.
Lair Action: Filth Blast
Ryle targets one creature he can see within 30 feet of him. A jet of putrid filth (or sweet smelling flowers) tethers Ryle to the target. Whenever Ryle takes damage, the target must make a DC 18 Constitution saving throw. On a failed save, Ryle takes half the damage (rounded down), and the target takes the remaining damage. This tether lasts until initiative count 20 on the next round or until Ryle or the target is no longer in Ryle's lair.
Lair Action: Ooze Fountain
Part of the ceiling collapses above one target that Ryle can see within 120 feet of it and a shower of soda floods down. The target must succeed on a DC 15 Dexterity saving throw or take 7 (2d6) bludgeoning damage and and be engulfed in goo. The engulfed target is restrained and unable to breathe. A target can take an action to make a DC 10 Strength check, ending the engulfed state on a success.
Lair Action: Swarming Insect Cloud
A cloud of swarming insects fills a 20-foot-radius sphere centered on a point Ryle chooses within 120 feet. The cloud spreads around corners and remains until Ryle dismisses it as an action, uses this lair action again, or dies. The cloud is lightly obscured. Any creature in the cloud when it appears must make on a DC 15 Constitution saving throw, taking 10 (3d6) piercing damage on a failed save, or half as much damage on a successful one. A creature that ends its turn in the cloud takes 10 (3d6) piercing damage.