This spell costs {X} less to cast, where X is the number of Mountains you control plus the number of cards with a cycling ability in your graveyard.
Search your library for a Dragon or Phoenix card, put it onto the battlefield, then shuffle.
Mountaincycling {2}

Bring Down the Sky deals X damage to each creature and each planeswalker. Put up to X exiled cards with flashback you own into your graveyard.

Choose one —
• Destroy target noncreature artifact with mana value X.
• Burn Up deals X damage to target creature or planeswalker.

Whenever this Subroutine runs, discard up to three cards, then draw that many cards.

Whenever this Subroutine runs, creatures you control get +2/+0 until end of turn. Target creature you control gains first strike until end of turn.

Calamitous War Cry deals 2 damage to each creature. If there are six or more different creature types among creatures you control as you cast this spell, it deals 2 damage to each creature you don't control instead.

Charge Beam deals 4 damage to target creature or planeswalker.
Amity — If you attacked with exactly two creatures this turn, Charge Beam deals 2 damage to that permanent's controller.

Choose one. If this spell's flashback cost was paid, instead choose three and you may choose the same mode more than once.
• Destroy target artifact.
• This spell deals 3 damage to any target.
• You may discard one or more cards. If you do, draw that many cards plus one.
Flashback {7}{R}{R}

Gain control of up to two target creatures with total mana value 4 or less until end of turn. Untap one of them. It gains haste until end of turn.

Enchant creature
Whenever enchanted creature deals combat damage to a player or planeswalker, you may sacrifice it. If you do, untap all creatures you control and after this phase, there is an additional combat phase.

Whenever a Subroutine you control runs, exile the top card of your library face-down.
{R}, Discard your hand, Sacrifice this enchantment: Put all cards exiled with this enchantment into your hand.

Crucible Takedown deals damage to target creature equal to the greatest mana value among permanents you control. Surveil 2.

Landfall — Whenever a land you control enters, exile the top card of your library. You may play that card until the end of your next turn.
{1}{R}, Sacrifice Crumbling Tower: It deals damage equal to the number of cards exiled with it to target player.

Destroy target artifact or land.
Flashback {4}{R}{R}

[+1]: Crux deals 1 damage to target player or planeswalker. Put a chain counter on up to one target artifact or nonbasic land. It loses all abilities except mana abilities as long as it has a chain counter on it.
[–2]: Discard a card. When you do, Crux deals damage equal to the discarded card's mana value to up to one target creature and you draw a card.
[–6]: Exile target red instant or sorcery card from your graveyard. Add {R}{R}{R}, then you get an emblem with “You may cast copies of the exiled card.”

Exile all creatures and all cards from each player's hand. Any player may play those cards during their turn for as long as they remain exiled, and mana of any type can be spent to cast those spells.
Exile Dawn of Peace.

You may choose this spell's targets at random. If you do, it costs {2} less to cast.
Return target instant or sorcery card from your graveyard to your hand.
Flashback {6}{R}

Equipped creature gets +2/+0.
Whenever equipped creature attacks, make a pledge.
Equip {3}

When Desolate Lands enters and whenever you cast a spell, it deals 3 damage to target opponent unless they sacrifice a permanent.

Draconic Ire deals 3 damage to target creature or planeswalker.

Target creature gets +2/+0 and gains first strike until end of turn. If it's a Dragon, put a +1/+1 counter on it.

Create two 1/1 colorless Thopter artifact creature tokens with flying, then each Thopter you control deals 1 damage to each opponent.

Create a Solidarity token. When you do, pay for and choose any number.
+{R} — Edgeland Pledge deals 2 damage to any target.
+{U} — Tap up to three target creatures.
+{G} — Create a 1/1 red Soldier creature token. It gains haste until end of turn.

Corrupt — Electronic Countermeasures deals 5 damage to target creature or planeswalker. If you control a permanent with greater mana value than this spell, exile the top X cards of your library, where X is the excess damage dealt this way. You may play those cards until your next end step.

Choose one —
• Elektes's Charge deals 2 damage to each nonenchantment creature.
• Up to two target creatures you control each get +2/+0 and gain trample until end of turn.