I'm using this paper 2d framework of UE4 where a plane mapped with sprite texture is put in 3d world and therefore appears as 2D when viewed from sideways.
Its all good for games like NES mario where other than jumping you can only move along X axis.
However if you look at games like double dragon and Battletoads they have an isometric perspective and a virtual third co-ordinate axis which points outwards from the screen towards the player, you walk along this with d-pad up and down. It also works for objects in the scene such as a box or ladder which you can climb up and down along this axis, it also affects the game logic say like where your character's landing point would be when you jump.
how would you go about implementing this using 3d planes mapped to 2d textures without making some virtual co-ordinate system of your own?