Rain is one of the faces of MK1 changes. If you know him from previous games, you need to re-discover this character. And that includes his story and fighting mechanics.
A lot of basic information was discovered during Kombat Kast 3, where the Mortal Kombat developers break down some basic features of Rain. Now, when the game is out (for early access), we can finally see what pro players can do with those re-imagined abilities.
HeeyGeOrge has proved that Rain may be quite a promising pick — if you like devastating combos. Here are tweets with impressive corner combos.