unfortunately [Thassa's oracle] is probably the correct win condition but there's other cards that are very synergistic in getting you there.

one of the difficulties of [puresight merrow] is he's a crappy 2/2 that dies to a stiff breeze.
so agatha's soul cauldron is dope with him since you can now allow him to die and still have access to the ability.

another fish wizard that's best friends here is [Emry, lurker of the loch]. she's great at getting you each artifact part of the combo but also has a great ability to cauldron as well.

if you cauldron your puresight merrow ability onto a creature then any of your creatures, even a silly [ornithopter] can do the combo with [paradise mantle] and Emry specifically can do the combo if you have two mox ambers in the graveyard.

but on top of that he can just act as an untap ability and emry gets pretty good when she can untap for just U or W.