It's a fantasy role-playing game.

DM: You are Keyleth, a half-elf druid . You are the member of the famous group of adventurers. Previously, Scanlan, who was in front of you, quickly casts Dominate Monster and succeeds in taming the gloomstalker. With it now under his control, he names it Mr. Mistoffelees and orders it to call off the hunt.
DM: Okay. Natural 19 plus three. So, as you shift down into the tiny mouse-like form, its claws immediately slam into and sink into the mouse body. Yeah, that's a 23 to hit.
Player: Yeah. Immediately poof.
DM: How much hit points does your mouse form have? Like one?
Player: I'm assuming no more than a kitten's worth.
DM: Right, so yeah. So, we'll say for the purposes, one. So that would be 16 points of piercing damage, so your form immediately reverts, its claws now fill with your regular Keyleth form. You take 15 points of piercing damage, Keyleth, and you are grappled.
Player: Cool. Cool. Cool. Cool story. Cool.
DM: As soon as it grabs you, it begins to pull you out of the tunnel and lift with you in its claws.
