PLEASE NOTE: The writeup is for an older version of this deck. I was just too lazy to update my strategy writeup when I updated the decklist. Writeup will be coming soon...
The Plan A for the deck to win is (1) ramp hard early, (2) get Sisay out, (3) tutor for protection and, (4) bring out the finishers to close out the game. Use spot removal when necessary. As you all know, Plan A (almost) never happens at a multiplayer table. I often end up electing to bring out the hatebears and control pieces to slow the game to the pace I want and then tutoring for game ending threats at the end. Of the five decks I run (Sisay, Bruna, Creature Teferi, Keranos, and Lin Sivvi) this is by far my best deck. It is my EDH pride and joy. It helps me win a lot of games and is a blast to pilot. I love having an answer for nearly every situation.
If left unchecked, this can function as an aggro deck that just ramps hard and brings out beefy angels to end the game. However, aggro is not viable at competitive tables. Instead I generally find myself seeking to slow my opponents' games down to a crawl as much as possible with little interference to myself. Hence why I don't run Kataki or Hokori. I tried to pack as much removal in the deck as possible. Instant speed Nature's Claim, Beast Within, Path to Exile, and Swords to Plowshares make sure anything really dangerous is taken care of quickly. Erratic Portal + Mangara of Corondor is one of my favorite removal combos to allow me to re-use Mangara throughout the game. This usually allows me to take out 3-4 permanents before someone decides to take Mangara or Erratic Portal away from me.
Crop Rotation is great utility, especially to fetch for Strip Mine to put in the Strip Mine/Crucible lock. Constant Mists is also crazy good with Crucible of Worlds, Azusa, Burgeoning, and Exploration.
I like to use taxing effects like Ghostly Prison, Windborn Muse, and Old Thalia with hatebears like Gaddock Teeg, New Thalia, Linvala, Dosan, and Dromoka to limit my opponents' ability to carry out their game plans and/or screw with my game. I try to be prepared to defend myself at all times whether with spot removal, board wipes, or pillowfort/deterrent cards. If I'm in for a longer war of attrition, I'll bring out Ghostly Prison and/or Windborn Muse to allow me to build up my board while forcing attention elsewhere.
The other thing I love to do is abuse the hell out of Sisay's tutor mechanic. Thanks to Thousand-Year Elixir, Paradox Engine (!!tutorable by Sisay!!), Illusionist's Bracers, Umbral Mantle, and Seedborn Muse, this is never a problem. My meta runs a ton of theft and they love to try and steal Sisay from me. So Worldly Tutor, Eladamri's Call, and Fauna Shaman give me plenty of tutor options in the event that Sisay gets stolen or shut down and otherwise still allow me to access any of my non-legendary creature toolbox.
The win conditions are (1) Kamahl, (2) Elesh Norn, and (3) Avacyn. If all else fails and I just need a beater to win through combat I fetch Akroma and go to town. I do like having as many relevant and worthwhile Angels in the deck as possible as an homage to my favorite creatures when I started playing MTG years ago. Sun Titan I pull out as a beatstick when I need to come from behind and rebuild my board. An alternate win con is Linvala and/or Elesh Norn + Kamahl, Fist of Krosa. I only do that when the game is really cut throat or when someone really pisses me off. I can also go infinite with Selvala, Heart of the Wilds equipped with Umbral Mantle to make infinite mana and overrun the table using Kamahl's activated ability.
The looks on my opponents' faces when I use Austere Command or Mageta the Lion with Avacyn out are priceless. Recursion is based around Eternal Witness, Loyal Retainers, Sun Titan, Bow of Nylea, Crucible of Worlds, and Mistveil Plains.
All critiques and suggestions for improvements are welcome. Considering Living Plane, but I am concerned about having Elesh Norn or Linvala stolen from me. Also considering Rings of Brighthearth for extra tutor power; Michiko Konda, Truth Seeker as a deterrent creature, and Primal Command primarily for the graveyard utility. However Primal Command's CMC exceeds Teeg's restrictions which makes it unlikely that I would include a utility card like that. Any non-creature card with 4 cmc or more has to be really valuable for me to to include it as I almost always put Teeg out every game.