[@The Muse] My idea is an assassin so my thoughts were maybe Hecate(goddess of magic),[s] Aeolus or Zephyrus(both gods of wind,  Zephyrus is just below Aeolus and somewhat answers to him)[/s], or Nyx(goddess of night)
[hr]Edit: Struck out the gods of wind cause I couldn't come up with anything ability-wise for them other than wind control and I didn't really like that. 

For Nyx I was thinking either like night vision or possibly shadow walking now that hades is using that

Then for Hecate I was thinking healing magic of a sort because it would oppose the nature of an assassin to be a healer, but that could also fall under the greek god Asclepius. 

Another idea I gained through Asclepius is a minor goddess, who is also his daughter, Panacea. Panacea is the goddess of universal remedy aka medicine which could lead to the ability knowing knowledge they didn't know before regarding herbs for medicine and other things required for that and just knowing how to make them and what medicine treats what.