There are a few key differences, like that split cards have the combined mana value and types of both halves, while MDFCs only have the properties of the front half when anywhere other than the stack or the battlefield
(Plus Merlin, Shapeshifter in his own human form.) Each of the shapeshifting Merlin cards offers a different boon when they first arrive on the table and when they leave, presenting the opportunity to combine them with cards that cycle them in and out of your hand to stack up the benefits
When I examined it before, it was just Secret Lairs and was more about how they were going to do them
I think I like Necro-brand, lets go with that
Looking to Moderns Primeval Titan decks, the Dryad has a lot of competition from Azusa, Lost But Seeking, Oracle of Mul Daya, Wayward Swordtooth, and Courser of Kruphix
There are four Summon creatures in the deck that you could essentially keep around forever with the right counter shuffling