This datapack is just close enough to my Morph Datapack that I made, but there is a whole bunch of changes in the functions and code.

Firstly, you need to kill a mob for it to be activated, every mob also still has it's ability, but now you need to like sneak to activate it or jump to activate/switch abilities, etc.

You can crawl as a Spider by sneaking while looking at a block, you can explode as a Creeper by sneaking while looking straight down, you can teleport as an Enderman by sneaking where ever you are looking at, you can even switch between the distance of the tp of an Enderman by jumping, you can even morph into Warden itself and use it's abilities, etc.

Q. How do I start the datapack when I load into the game?
A. You need to be in survival/hardcore to begin, first you need to run this command: /function morph:start for it to be activated, then you need to start killing mobs for you to be able to morph into them.

Q. What makes this different from your Morph Datapack?
A. In this datapack, you need to kill mobs for you to transform into them, BUT you can NOT transform into these mobs again: EnderDragons, Withers, Blocks, Items, Minecarts, Boats, Item Frames (Glowing ones too), Armor Stands.
Also in this datapack, every item that is usable is removed, you can not be given an item in this datapack, not like Morph Datapack, instead you will need to Jump, Sneak, Look straight down, to activate abilities, but you still only get Snowballs for Blaze, Ghasts, Snowmans

Other than that, have fun with this datapack!