Sorry for necro this. But it is one of the first hits on google when you search for "mass polymorph edh". I have been doing a Talrand deck as well. I started out with a cutthroat version including Deadeye Navigator. I too decided that was boring. Instead I went for a theme with sea monsters.
I have had a lot of fun and wins with it and wanted to share. It works great in small casual playgroups. It is fragile to targeted removal and board wipes. But Expropriate mitigates this a bit because I get an extra turn before my opponents, and if I cast Synthetic Destiny in an opponent's end step I get two turns to wreak havoc with the sea monsters. And even if the sea monsters get wiped, Trench Gorger emptied my deck for lands so I have very effective card draws to search for alternative win conditions in the rest of the game.
I have had a lot of fun and wins with it and wanted to share. It works great in small casual playgroups. It is fragile to targeted removal and board wipes. But Expropriate mitigates this a bit because I get an extra turn before my opponents, and if I cast Synthetic Destiny in an opponent's end step I get two turns to wreak havoc with the sea monsters. And even if the sea monsters get wiped, Trench Gorger emptied my deck for lands so I have very effective card draws to search for alternative win conditions in the rest of the game.
I have a full list for anyone interested