how to move along Virtual Z axis in 2D games?

Hi, in 2D games you generally move along just two axes that is forward/backwards and jump up/down like in super mario brothers on NES.

However there are many 2D games that allow movement along a third virtual axis i.e. apart from jumping you can also walk up and down which gives the illusion of depth or isometric-ish prespective, examples from NES : double dragon games , Battletoads , TMNT , nekketsu kunio-kun games.

Does paper 2D supports something by default for movement along this virtual axis ?