The weakness of Griselbrand is that if you are too far behind when you make him you have to wait for him to deal damage before you can risk drawing cards and in this situation you are going to get wreaked by the right removal
Returning mechanics include Snow and Changeling, along with new ones like Foretell and Boast
Even though its convoke cost means it's a little harder to pull off if you're already going wide with a full board of creatures, being able to flash it into play at any moment can come in clutch during board wipes or if you need to keep a commander alive for another round
Etali, Primal Sickness gives players poison counters when it deals combat damage (in other words, infect) to a player, and a player loses the game with ten poison counters
Both these cards are old and won't be reprinted and while they're not needed in order to have a successful Shrine deck, having them will boost the power of the deck substantially
This set is surprisingly packed with interesting, powerful, and even just fun designs, given how parasitic the mechanics are (shrines, lessons, allies, etc.)