My point is that you cannot do cell shading in UE4 with lighting enabled. You can do cartoonish visuals, of course, but not something that resembles 2D due to the way the lit materials work. Well, you *can*, but that would require either hacking the physically based deferred renderer as to change the entire BDRF or adding a new "shading model", but you'd probably end up with crappy looking post process cell shading. GGXrd's way is much more elegant and actually gives artists control over the cell shading output. It's also damn easy to program.
Smash runs at spitting distance from dropping the framerate, however. You can get slowdowns in many levels by pausing the game and zooming the camera a little bit, for example, since it makes some effects cover more pixels of the screen than they do during gameplay. Every object, transparency and foliage was placed and moved around to make it possible. It's also not a port of a game from higher end systems.
