msem-instigator

Cradle of Corruption enters tapped.
Whenever a creature dies, put a creation counter on Cradle of Corruption.
{T}, Remove ten creation counters from Cradle of Corruption and sacrifice it: Put up to two target creature cards from graveyards onto the battlefield under your control. Activate only as a sorcery.

You can't lose the game.
At the beginning of your upkeep, put Cradle of the Sun on the bottom of your library and your life total becomes 4.

Crafted Coast enters tapped unless another player controls a land that could produce {W} or {U}.
{T}: Add {W} or {U}.

{T}: Add {C}.
{3}, {T}: Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Cresting Bay enters tapped unless you control a basic Island.
{T}: Add {U}.
{2}{U}{U}: Until end of turn, Cresting Bay becomes a 3/3 blue Elemental creature with “Whenever this creature attacks, you may draw a card then discard a card.” It's still a land.

Flying
At the beginning of combat on your turn, create a 5/5 red Dragon creature token with flying and haste. That token attacks this combat if able.

You may have Crossroads Town enter tapped. If you do, search your library for a basic land card, reveal it, then shuffle and put that card on top.
{T}: Add {C}.

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell with a creature type no creature you control has.

Equipped creature gets +X/+X, where X is the number of cards in your graveyard.
Sacrifice a creature other than equipped creature: Equipped creature gains lifelink and indestructible until end of turn.
Equip {3}

Crumbling Aqueduct enters tapped unless you control another Desert.
{T}: Add {U} or {B}.

Crumbling Necropolis enters tapped.
{T}: Add {U}, {B}, or {R}.

({T}: Add {B} or {R}.)
Whenever Crumbling Precipice becomes tapped, you lose 1 life unless you control two or more basic lands.

Crumbling Shrine enters tapped. When it does, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this, then you may put that card into your graveyard.)
{T}: Add {G}.
{2}{G}{G}: Crumbling Shrine becomes a Nymph creature. (This effect lasts indefinitely.)

Crumbling Vestige enters tapped.
When Crumbling Vestige enters, add one mana of any color.
{T}: Add {C}.

{T}: Add {C}.
{X}: Crypt of Myriad Fates becomes a copy of target creature card with mana value X or less in your graveyard until end of turn, except it's 2/2 and a land in addition to its other types. Activate only outside of combat.

Puzzlebox (Begin the game with this and another card you own from outside the game in the command zone, locked. That card is face down until you unlock this.)
{1}, Discard two cards: Unlock Cryptic Fragment. If the revealed card is a basic land card, put it into your hand.

Cryptic Reef enters tapped.
{T}: Add {G} or {U}.
{2}{G}{U}, {T}, Sacrifice Cryptic Reef: Draw a card.

({T}: Add {U} or {R}.)
Whenever Crystal Cavern becomes tapped, you lose 1 life unless you control two or more basic lands.

Crystal Garden enters tapped.
{T}: Add one mana of any color. You can't spend this mana to cast a creature spell.

{T}: Add {C}.
{T}, Pay 1 life: Add {U} or {B}.

{T}: Add {C}.
{T}, Pay 1 life: Add {W} or {U}.

You may look at the top card of your library.
{T}: You may play the top card of your library.

Enchant player
At the beginning of enchanted player's upkeep, that player upgrades a creature you control. (They give it one of the listed counters it doesn't have.)
• +1/+1
• Lifelink
• Menace

({T}: Add {W} or {B}.)
Cursed Wastes enters tapped.
{1}, {T}: Add {W}{W} or {B}{B}.

CySec Nexus enters tapped.
{T}: Add {W} or {U}.
{W}{U}, {T}: Create a Function token with “Flash.” Activate only as a sorcery. (It's an enchantment. As you cast an instant or sorcery spell, sacrifice any number of Functions to add their effects to that spell.)