The Hylden Lord (Legacy of Kain) transforms the body of Mortanius the Necromancer into a hulking beast.
The Transformed (Legacy of Kain: Defiance) are the result of Hylden spirits transforming their human hosts into monstrous shapes.
Freddy Krueger (A Nightmare on Elm Street) gruesomely transforms Jesse Walsh's body into himself as he possesses him.
The Leviathans (Supernatural) can shapeshift their host bodies into anyone else by sampling DNA.
Agents (The Matrix) are capable of taking over the bodies of anyone still plugged into the Matrix, "overwriting" them in order to physically manifest and deal with the Resistance.
Diablo (Diablo III) manifests as the Prime Evil after possessing the body of his daughter Leah.
After possessing Barry Kahn, Watagash (Dragon Ball Super) transformed his body in different stages, the first simply making him more muscular...
...the second mutating him into a larger, ape-like creature...
...and the final turning him into a giant monster with no resemblance to his original form.