The strategy of the deck is to do one of two things: Aggro attackers that can be protected and copy Archangel Avacyn/Avacyn, the Purifier's triggered abilities.
The aggro plan: Cathar's Companion, Ember-Eye Wolf, and Sanguinary Mage. Temp pump by abilities, Make a Stand, and Rush of Adrenaline.
The Avacyn plan:
Archangel Avacyn similar effects are- Nahiri's Machinations, Make a Stand, Cathar's Companion triggered ability.
Avacyn, the Purifier similar effects are- Kozilek's Return.
Utility cards: Eldrazi Displacer for spamming Archangel Avacyn's ability, Kozilek's Sentinel for a big butt with more potential damage, Chaplain's Blessing to outlast your opponent's onslaught.
Non basic lands: Battlefield Forge for the Displacer and fixing of course, Mirrorpool for the Displacer too with a clone/reverberate ability, and Westvale Abbey for again Displacer mana, chump blockers late game and an Avacyn trigger with a demon coming out.
Sideboard: Angelic Purge for more Avacyn triggers and removal, Chandra, Flamecaller for more bodies to the Abbey or loot ability or one sided board wipe; Chandra didn't make mainboard due to timing issues, Eerie Interlude for more one sided board wipe situations and Archangel Avacyn triggers, Feiry Temper for more removal while looting, Nahiri, the Harbinger is there for more looting or removal or tutoring. The sideboard loots more into threat rather then protects your creatures while wiping your opponents.
Eldrich updates: Mirrorpool will be replaced with Hanweir Battlements due to the latter being more versatile for this build than the former. Next up getting the axe is either Sanguinary Mage or Kozilek's Sentinel for Hanweir Garrison. For me Kozilek's Sentinel gets the axe due to the lack of survival in game. Plus Hanweir Garrison can meld in response to removal with Hanweir Battlements. But if you want flavor keep with the Kozilek/eldrazi taking over theme then keep Kozilek's Sentinel for that. Now here are possible yet improbable adds to the deck are the Brisela combo because it's too slow however a Gisela or two might help in certain match ups. And finally Thalia, Heretic Cathar almost makes the mainboard add but doesn't because she can be killed easier than the Cathar's Companion. However I think she overthrows Nahiri and causes me to restructure my sideboard a bit to have more of a removal sideboard with no looting.
Post rotation/replaceable pieces: Kozilek's Sentinel is replaceable for whatever just need something out of bolt range, Rush of Adrenaline could become replaced by Expedite for faster aggro play and a cantrip; I just haven't tried it due to the extra damage Adrenaline Rush gets in, Magmatic Chasm is here for the same reasons and could be replaced by Expedite as well and would be cut before Adrenaline Rush, Battlefield Forge with rotate out and become Warped Landscape or Needle Spires.
