If you choose the blue path, the "Path of Wisdom," your Seeded Booster Pack will focus on blue and you might be able to get a nice Triton theme going. Tritons being Theros's Merfolk.
I love the new Master of Waves, though he boosts Elementals and not Merfolk, he gives you an Elemental army equal to your devotion to blue when he enters the battlefield.
If you look at the art, the waves that are cresting around him are actually shaped like creatures; those are his Elementals that he created when he entered the battlefield!
In fact, check out the Elemental token in Theros!
And the flavor going on here is awesome. These are waves he has stirred up to be powerful weapons but as soon as he is gone, the force controlling those waves disappears and those waves fall back to the flat sea - a temptestuous ocean becomes calm and tranquil once more.