Swallowed Whole

You are Pinned inside a creature's stomach. As long as you remain Pinned, you suffer the creature's Stomach Acid at the start of each of your turns. If you reduce Pinned to Grappled, then you crawl out to its mouth.
Swallowed creatures can make attacks against the monster's Gut AC. Once they have done damage equal to the monster's Gut HP, they create a hole they can crawl out of. They have Advantage on Checks to climb out through this hole, and are fully freed from the grapple if they succeed. Additionally, the monster suffers Bleeding Guts.