Smoke stays mostly the same as in MK3, while gaining advantage of using combo started from the air combo. He is not a secret character anymore and can be choose in the character selection screen.
Smoke has useful special move that can be easily mixed. His spear can catch opponents anywhere except if they are crouched. His Teleport Uppercut is a deadly way to start a string of combos and his Air Throw is often used as a combo ender or as a counter. Lastly, he has the ability to turn invisible and stay that way until he is hit.
Against the CPU, Smoke can trick them with a jumping kick so he can start his combo string with the Teleport Uppercut and Spear. He is also able to do a jump kick or jump punch and Air Throw his opponent right after, as long as he is very close to them. His combo is strong and is used either as a starting jump punch or with the spear. His invisibility moves, however, is completely useless, since the CPU know your location regardless of your visibility.
As a side note, Smoke can perform his Teleport Uppercut twice against Shao Khan, but not against any other character in the game. Having the same move, Sektor can do it as well. It is probably an oversight and not an intentional ability.
TAS tools were used to make this high quality playthrough video.