Injustice 3: 10 Supervillains NetherRealm Must Include
2. Upside-down Man
One of the more recent additions to the DC Universe, the Upside-down Man first appeared in James Tynion IV's ongoing Justice League Dark series. Being a magical creature from the also newly-introduced otherworld and a very powerful one at that, seeing him join the roster of Injustice would be excellent.
The character has proven his abilities by completely decimating the magical branch of DC's premiere team, using his mind-bending, reality-warping abilities - which would make for some wild fights.
Unlike some of the villains on this list, Upside-down man would provide an incredible, new direction for the Injustice-verse, and help to introduce some of the more mystical elements into the game (and, fingers crossed, lead to the addition of heroes like John Constantine).