No Elven Mystic available, but that part of Standard seems to be permanently over. However, there is several fairly efficient manaproducers in the format, like Servant of the Conduit and Rishkar, Peema Renegade and then there’s these two:
There’s also Kiora, Master of the Depths, which might work, but I wouldn’t bet on it.
So, what do we ramp into?
Here’s a few ideas:
Since there’s already a beginning of a energy theme, we might do that as well.
… and finally, Nissa, Steward of Elements.