The obvious green sideboard card would be Abrupt Decay, and depending on the meta at your LGS you might even want to mainboard it. Choke is also a very good option against decks such as Twin or Delver. I feel like Archangel of Tithes doesn't give you the high-end creature you're looking for in a deck like this, but go ahead and tell me if I'm wrong.

I'm not really looking for a game-ending creature with Archangel of Tithes. I want my tokens to be able to do the job. Archangel is there to help control the board state post-Turn 4. Turn 4 is when a typical Modern deck should kill, but if I can disrupt the hand enough, I can survive, and that's where the brunt of the tokens start to come out. Basically Archangel is there to act like a Ghostly Prison, staying untapped and not attacking until the moment when I can end the game with token creature damage. Large amounts of flying creatures are difficult enough to block, but this should put the nail in the coffin.

I am also considering Hero of Bladehold and Angel of Jubilation for a 4-drop creature slot. Hero's Battle cry and token spawn are both pretty awesome, and Angel gives an anthem as well as providing a useful niche ability. It may not matter as much to compliment the deck's strategy as it does to keep me alive until I can win. But I still have some more testing to run.

What is the purpose of Flagstones of Trokair?

Flagstones of Trokair is a pseudo-fetch land. This deck is almost exclusively white mana-intensive, so the only lands I would really need to produce black are the Godless Shrines. When Flagstones comes out, it's effectively a Plains until I draw into another one. Then I set out the second Flagstones, and because it's a Legendary Land, I have to destroy one of them, so I get rid of the second before it resolves. When it hits the graveyard I can then use its ability to search for a Godless Shrine or another Plains.

Ah right, it's legendary. That's cool.

It is cheaper than a second playset of fetches, it doesn't cost any life (which if I end up running Angel of Jubilation is a big deal), but it's way harder to find.

I like Sanctimony in white SBs. It's a (kind of) harder to get rid of Kor Firewalker, plus if an opponent taps more than one Mountain to cast a spell, you get more benefit than just the on-spell trigger of the Kor.

I have considered Sanctimony as well. While I agree that it would be hard to remove (red has little to no enchantment hate), I can use Kor Firewalker or Auriok Champion to continuously block creatures like Monastery Swiftspear, Goblin Guide, and Vexing Devil. Those creatures can sometimes do more damage than the burn spells themselves. That's why I keep it in.

I would recommend against flagstones. If they didn't come into play tapped they would be fine for what you are intending, but unfortunately they do. Tidehollow isn't very good in this meta, I would highly recommend taking it out. Take out archangel of tithes as well. Instead of sideboarding auriok, main her. Add 1 Raise the Alarm/Secure the Wastes. Your side needs some work as well. What is your local meta?

Also you need Thoughtseize.

Flagstones doesn't come into play tapped. I think youre confusing it with Windbrisk Heights, which I have 2 of in here. The reason I went Tidehollow over Thoughtseize is because the latter doesn't help me against my local meta, which is Red Deck Wins. Not saying it's bad, but it makes their job easier. I am considering maining Auriok, but I just dont have her right now. I have 3 shops near me and none of them have her. I might replace one Zealous Persecution with one Raise the Alarm, but I never get to the point in the game where I have a mana sink for Secure the Wastes to be viable IMO.

The reasoning for Archangel of Tithes is that I wanted something able to survive a mass damage-dealing board wipe like Anger of the Gods or Languish (neither are hugely Modern popular but you get the idea) and wouldn't become useless once all my tokens were gone. It's sort of a last line of defense if my initial strategy doesn't go as planned.

No, I'm talking about the plains that comes in from Flagstones.And tidehollow is still bad against RDW. Just run Duress over Tidehollow Sculler then. And it depends on your meta. Against midrange decks Secure the Wastes can be very useful, but it can depend on the meta.

Hero of Bladehold is a much better choice then. Almost no one runs Languish, so you don't have to worry about that.

I still have yet to playtest Archangel + Tidehollow vs Auriok + Thoughtseize. I'll give your other suggestions some playtesting as well. Thanks!

Trust me, Archangel has no place here. If you want a 4 drop creature you can't beat Hero of Bladehold. And no problem!

Ah, I see what you're saying about Flagstones now. I'll probably just replace those with the Flooded Strands I have then, or maybe Windswept Heaths if I decide to splash green. Hero of Bladehold is also in the running for my 4-drop creature slot, along with Angel of Jubilation. Right now the only one I actually own is Archangel, because apparently Hero is just as hard to find as Auriok. When I did testing with Hero, it was cool when she worked, but that wasn't often. I think i'm just going to get a stats page going, maybe that will help this decision.

To Microsoft Excel! flies away

Flooded Strand or Windswept Heath are both good choices. I would advise against splashing green personally. Angel of Jubilation should be out of consideration as well. She doesn't pass the bolt test, and unlike Olivia Voldaren, she can't get herself out of the range of bolt.

Maybe if I end up maining Auriok, I can side board Archangel for the Tokens and Twin matchups?

No, because then there are better options like Zealous Persecution or Ghostly Prison.

I was thinking about green because I could expand my sideboard a bit, but I also thought I could find some powerful anthem, like Collective Blessing but viable. So far the best I could find was Sigil Blessing, but nothing worth the splash for. And yeah, the only way Jubilation could live through Bolt is if I had a Honor of the Pure out, and that's not likely. I could replace her board slot with something like Hallowed Moonlight.

Ah, forgot about Ghostly Prison.

Also Archangel does nothing to stop twin. And the only thing in the color green worth splashing for is Gavony Township or Abrupt Decay, but we already have Vault of the Archangel.