NOTE: I didn't know where to put this, so I put it in the mods section. Mods, feel free to move this to the correct location.
VanillaMorph is a minecraft vanilla command block contraption which allows you to morph into any mobs (Which don't fly) by simply walking into them!
The installation method is simple: Just copy and paste the command, or download and load the structure to a structure block (More information here).
The link above redirects you to my website, which in there you can find detailed install instructions, as well as downloads to the commands and the structure NBT files as an updating set of commands, and also the source of the files.
The Structure Block form
The One Command form
Morphed to a creeper (Ignore the weird scoreboard...)