Strive — This spell costs more to cast for each target beyond the first.
Any number of target creatures each get +1/+1 and gain indestructible until end of turn. (Damage and effects that say "destroy" don't destroy them.)

[+1]: Each opponent discards a card and loses 2 life.
[−3]: Gain control of target creature until end of turn. Untap it. It gains haste until end of turn. Sacrifice it at the beginning of the next end step if it has converted mana cost 3 or less.
[−8]: Each opponent loses life equal to the number of cards in their graveyard.

Enchant your library
Enchanted library is an artifact creature on the battlefield with power and toughness each equal to the number of cards in it. It's still a library.
If enchanted library would leave the battlefield, exile Animate Library instead.

, Pay 1 life, Sacrifice Arid Mesa: Search your library for a Mountain or Plains card, put it onto the battlefield, then shuffle your library.

[+1]: Create a 2/3 blue and black Nightmare creature token with "Whenever this creature attacks or blocks, each opponent exiles the top two cards of their library."
[−3]: Return target nonland permanent to its owner's hand, then that player exiles a card from their hand.
[−7]: You may cast up to three spells from among face-up cards your opponents own from exile without paying their mana costs.

Target creature gets +4/-4 until end of turn.

Banefire deals X damage to any target.
If X is 5 or more, this spell can't be countered and the damage can't be prevented.

Sliver creatures you control have menace. (They can't be blocked except by two or more creatures.)

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom of your library in a random order.)
Bituminous Blast deals 4 damage to target creature.

, Sacrifice a creature: Blood Rites deals 2 damage to any target.

Haste
Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom of your library in a random order.)

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Flying
Whenever another creature enters the battlefield under your control, target creature gets +2/+0 until end of turn.

Draw four cards, then choose X cards in your hand and discard the rest.

Whenever you cast a spell from your graveyard, Burning Vengeance deals 2 damage to any target.

Choose a nonland card name. Target player reveals their hand and discards all cards with that name.
Flashback—Sacrifice a creature. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Devour 1 (As this enters the battlefield, you may sacrifice any number of creatures. This creature enters the battlefield with that many +1/+1 counters on it.)
When Caldera Hellion enters the battlefield, it deals 3 damage to each creature.

When Canal Courier enters the battlefield, you become the monarch.
Whenever Canal Courier and another creature attack different players, Canal Courier can't be blocked this combat.

Landfall — Whenever a land enters the battlefield under your control, you may have target creature get -1/-1 until end of turn.

Put a +1/+1 counter on target creature.
Put a +1/+1 counter on target creature.