If you can set up a loop between Phyrexian Altar and Gravecrawler, Priest of the Crossing can provide infinite board-wide buffs
My partner and I ended up with a record of 1-1-1 (one win, one loss, one draw), mostly because the two-headed giant games were best-of-one, rather than the best-of-three youd usually expect in events like this
If you want the simplest place to start, build around Elder Deep-Fiend for tempo or Herigast for Commander
Those include cards featuring Prepared spells, which feel like a greatest hits of spells from Magics long and storied past, like Ancestral Recall or Demonic Tutor, a series of new Elder Dragons, and the awesome new Emeritus cycle
You can cast it from exile no matter what # you get, and then you can either spend mana to cast it with mana of any color usable and then you can get it for free with the higher roll
Doors of Durin is fun for the flavor of elves and dwarves working together