#1 Andrade Cien Almas
Probably the most ideal superstar to replace Rey Mysterio in any sort of place is going to be Andrade Cien Almas. Almas got promoted to the main roster along with his manager Zelina Vega but has failed to have a concrete feud on Smackdown.
Almas has proven his worth as a competitor in the ring with AJ Styles and Daniel Bryan. He has been meddling in the Miz and Bryan's rivalry and has often competed in mixed tag matches against Bryan and Brie, and with R Truth and Carmella.
Zelina Vega recently got injured which has left Almas off track but becoming the sole survivor could do wonders for his career moving forward, and being a heel, his manager can boast of this accomplishment for a long time. This could be the platform that Almas needs to reach the same height that he did on NXT.