Many of these cards, including Field of the Dead and Zombie Apocalypse, are likely meant to show off the effects of the Deadites that were capable of possessing the dead
Unholy Heat Unholy Heat is an interesting case: As long as you can fulfill its delirium clause, this red instant deals so much direct damage that it's basically unconditional removal something that red doesn't usually have access to, and which makes Unholy Heat a bit of a color pie break
The deck include 3 Talismans of the decks colors, helping to make up for the lackluster lands
Until this point, EDH players who wanted four colors would rule zero the Nephilim creatures from Guildpact , with their names still describing the color combinations
They changed Nadu around due to it being too strong
Quintorius Kand and Urianger Augurelt give you a little life for playing cards from exile, are enablers on their own, and have utility outside of those effects