I am trying to make a game where you turn into a rock which is a model. But I can't figure it out :/
I think the best way to do this is using a custom character.
You could create a character with your rock part as the torso, set the head transparency to 1, and remove the limbs from the model completely. This way, the player will appear as whatever your morph looks like.
The plugin page also links to a pre-made script for using the model in-game, so if you follow the instructions you should be good to go; I tried it myself.
Good luck!
No Problem, i asked a similar question about wow to make my player spawn with a certain piece of clothing. sadly i'm not sure how to make your person appear as a rock, but if you buy clothing that makes you look like a rock then you can use this script:
PlayerID = "98114558" -- The ID of the player who everyone would like it.
game.Players.PlayerAdded:connect(function (newPlayer) newPlayer.CharacterAppearance = "http://www.roblox.com/Asset/CharacterFetch.ashx?userID=" ..PlayerID newPlayer:LoadCharacter() end)
(you can change that ID that's mine :P)