1 Breeding Pool
1 Temple Garden
1 Hallowed Fountain
4 Steam Vents
4 Stomping Ground
3 Snow-Covered Island
2 Snow-Covered Forest
2 Snow-Covered Mountain
1 Snow-Covered Plains
2 Valakut, the Molten Pinnacle
4 Misty Rainforest

4 Sakura-Tribe Elder
4 Ice-Fang Coatl
1 Eternal Witness
1 Genesis

4 Arcum's Astrolabe

1 Path to Exile
2 Remand
1 Pulse of Murasa
1 Gifts Ungiven
1 Cryptic Command
1 Chemister's Insight

4 Search for Tomorrow
2 Scapeshift
1 Supreme Verdict
4 Bring to Light

3 Teferi, Time Raveler

Huntmaster of the Fells
Pia and Kiran Nalaar
Anger of the Gods
Force of Vigor
Force of Negation
Dovin's Veto
Crumble to Dust

The Bring-to-Light/Demonic-Pact shell wasn't good enough so we are spicing up (read: ruining?) a different BTL deck

The BTL-Scapeshift strategy is already well established, you have BTL to provide extra virtual copies of Shift that have a ton of extra utility for only 1 more mana, and the blue manabase gives you access to Coatl and Teferi which are both really good cards for the Scapeshift strategy.

Astrolabe is a relatively recent addition to the list (not my idea) but it does seem like it improves overall consistency by a lot
- Cycles (minor deck-thinning effect)
- Mana-fixes (Otherwise you are 4-colour deck playing 8 basics to enable coatl, sakura etc)
- Activates Coatl faster (extra Snow Permanents)
- Higher density of targets to bounce with Teferi for value
- P&K out of the SB can throw it at stuff

The spice here is the Gifts Ungiven package which includes the following cards:
- Pulse of Murasa
- Gifts
- Genesis
- Witness
- Jump-Start card (Chemister's Insight, or possibly Radical Idea)

Pulse of Murasa and Witness are acceptable without Gifts, Pulse is a nice tool to have maindeck against burn/aggro that does not have much opportunity cost in other matchups because it replaces itself. Most other BTL decks are already playing Timely Reinforcements in the side or even main. It also forms a pseudo-loop with Eternal Witness.

Eternal Witness is a fairly strong card in its own right but it interacts favourably with other cards in the deck:
- Witness + Pulse: Play Pulse, get back witness, play Witness, get back pulse, repeat
- Witness + Cryptic: Play Cryptic, counter opponent spell and bounce Witness. Play Witness, get back Cryptic, repeat.
- Witness + Teferi: Play Witness, get back Teferi from the yard, play Teferi, minus-3 and bounce Witness
When you have 2 graveyard-returning cards (i.e. witness and pulse) you can make Gifts piles of e.g. Pulse, Witness, X, Y, and you will eventually be guaranteed to be able to cast X or Y

Genesis isn't really seeing any play in Modern since its introduction in Modern Horizons but it does a decent role in this deck as a repeatable source of card advantage. Sakura/Coatl/Witness are all good things to be returning. When you have a Jump-Start card in your deck you can guarantee Genesis goes to the graveyard after you Gifts for it, and a pile of e.g. Chemisters Insight, Genesis, Witness, X seems good in a situation where you are low on resources and need to fire off a BTL to fight back into the game.

What are the opportunity costs for including this?

Some lists play 2-3 extra removal spells, like up to 2 Path + 2 Bolt or a miser Lightning Helix etc, this is the most significant loss but it's not uncommon for some lists to play e.g. only 2 path and no bolts. (Especially those lists that are also playing Astrolabe, typically compared to the original non-Astrolabe version they trim 1 land and then 2-3 pieces of interaction to fit the Astrolabe in the deck). We still have 1 Path and the 2 Remand for interaction and Pulse of Murasa helps to fight aggro to some extent. Witness is ok at blocking, but against decks like Vizier combo or Infect we will be worse.

Some lists play a card advantage spell like Drawn from Dreams, this is a clean swap with Gifts Ungiven.
Some lists play 1-2 extra copies of Cryptic Command.
Some lists have extra BTL one-ofs, most commonly Mwonvuli Acid-Moss and Ojutais Command. The modes of command don't offer anything individually unique, as draw 1, return a creature, counter spell, gain life are all covered by Cryptic and Pulse of Murasa. Swapping it with Chemister's Insight doesn't change the manacurve but it does lower the density of interaction in the deck again. Acid Moss is uniquely strong in some situations but against many decks where it is most effective it gets superseded by Crumble to Dust after sideboarding.

SB space is kind of tight but the plan is to have more targeted cheap interaction to help reach the lategame against combo decks (e.g. Force of Negation, Sudden Shock, Fry). The gifts/genesis plan should help to build up resources to win with Valakut even if we have to make trades to survive the earlygame.

One option is to play an unburial rites SB plan but I don't think there is any deck in the metagame where this makes sense. It takes multiple SB slots, and having only 1 copy of Gifts means that most likely it will have to go through BTL which makes it fairly slow. I don't think there is a deck currently that gets KO-d by eg Elesh or Iona that can't be effectively addressed by other means but I guess it's something to be aware of. (The way the deck is set up currently, there are already powerful ways to stabilize and/or lock up the game once you reach 4-5 mana, I think the problem is more likely going to be actually reaching that point in the first place).

Anyway, as usual I appreciate any thoughts/comments