You may pay rather than pay the mana cost for spells you cast.

Flash
Whenever a creature you control dies, each opponent sacrifices a creature of their choice.

Double strike
Whenever another legendary creature you control enters, put a +1/+1 counter on Gimli.
Whenever Gimli deals combat damage to a player, create a Treasure token.

: Untap all creatures you control. After this main phase, there is an additional combat phase followed by an additional main phase. Activate only as a sorcery.

: Add .
, Sacrifice a creature: Add .

Reach
Modified creatures you control have trample. (Equipment, Auras you control, and counters are modifications.)
Whenever a modified creature you control deals combat damage to a player, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Flying
When Thor enters, exile target Equipment, instant, or sorcery card from your graveyard. Until the end of your next turn, you may play that card.
Whenever you cast a noncreature spell, Thor deals damage equal to that spell's mana value to any target.

When you cast this spell, target opponent exiles the top half of their library, rounded up.
Ward—Sacrifice two permanents.
Ulamog enters with a number of +1/+1 counters on it equal to the greatest mana value among cards in exile.
Ulamog has annihilator X, where X is the number of +1/+1 counters on it.

Flash
Flying
When Vendilion Clique enters, look at target player's hand. You may choose a nonland card from it. If you do, that player reveals the chosen card, puts it on the bottom of their library, then draws a card.

Decorated cards in your hand have miracle . (Decorated cards include premiums, promos, and cards with alternate frames or art.)
At the beginning of your upkeep, if you control twelve or more decorated permanents, you win the game.

At the beginning of your upkeep, if an opponent controls more lands than you, you may search your library for up to three basic land cards, reveal them, put them into your hand, then shuffle.

Flying
You may reveal the first card you draw each turn as you draw it. Whenever you reveal an instant or sorcery card this way, copy that card and you may cast the copy. That copy costs less to cast.
When God-Eternal Kefnet dies or is put into exile from the battlefield, you may put it into its owner's library third from the top.

Split second (As long as this spell is on the stack, players can't cast spells or activate abilities that aren't mana abilities.)
Choose any number of target creatures with equal toughness. Destroy the chosen creatures.

Flying
: Choose a color. Creatures you control gain protection from the chosen color until end of turn. Activate only if this card is in your graveyard.

, Pay 1 life: Add or .
, : Mount Doom deals 1 damage to each opponent.
, , Sacrifice Mount Doom and a legendary artifact: Choose up to two creatures, then destroy the rest. Activate only as a sorcery.

Flying, ward
This creature enters prepared.
Whenever this creature attacks, you may exile eight cards from your graveyard. If you do, this creature becomes prepared.

+1: Create a 1/1 white Soldier creature token.
+1: Target creature gets +3/+3 and gains flying until end of turn.
−8: You get an emblem with "Artifacts, creatures, enchantments, and lands you control have indestructible."

Counter target spell.

(: Add or .)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Flying
Whenever Captain Marvel enters or attacks, exile up to one target creature. That creature's controller gains life equal to its power.
Whenever a creature other than Captain Marvel is exiled from the battlefield, you gain life equal to its power.