Poseidon, for Troll Lord Games' Castles & Crusades: Of Gods & Monsters by Jim Ward.
Poseidon is the god of the sea, depicted with his signature trident and as a merman.
This was definitely the most time-consuming. I'm a tad burned out right now, head spinning... tomorrow hopefully I can start/finish Hermes, which is highly unlikely...
Thanks again Jason for the hand reference!