msem-instigator

Clocktower Hideout enters tapped.
When Clocktower Hideout enters, look at the top card of your library. You may put it into your graveyard.
{T}: Add {B} or {R}.

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.)
Tap four untapped creatures you control: Unlock Clockwork Astrolarium. If the revealed card is white, put it into your hand. Otherwise, put it on top of your library.

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

({T}: Add {U}.)
Cloudbank enters tapped.
When Cloudbank enters, target creature gains flying until end of turn.

Cloudcover Heights enters tapped unless you control a Forest.
{T}: Add {R} or {W}.

({T}: Add {R}.)
As Cloudpeak Spires enters, you may pay 1 life. If you don't, Cloudpeak Spires enters tapped.
Basic lands you control have “{T}: Add {R}.”

({T}: Add {R} or {W}.)
Cloudsteel Summit enters tapped.
{1}, {T}: Add {R}{R} or {W}{W}.

{T}: Add {C}.
{1}: Clutch of the Coil becomes a 1/1 Snake creature with poisonous 2 until end of turn. It's still a land. (Whenever this creature deals combat damage to a player, that player gets two poison counters.)

({T}: Add {W}, {U}, or {B}.)
Coastal Dominion enters tapped.

Coastal Metropolis enters tapped unless you have 15 or less life.
{T}: Add {W} or {U}.

{T}: Add {C}.
{1}, {T}, Return Collapsing Ground to its owner's hand: Add one mana of any color.

{T}: Add {C}.
{T}, Pay 1 life: Add {B}.
{5}{B}, {T}, Sacrifice Collapsing Ridges: Return target creature card from a graveyard to the battlefield under your control. Activate only as a sorcery.

Combined Generator can't be blocked except by three or more creatures.

Enchant creature
Enchanted creature must be blocked if able.

{T}: Add one mana of any color in your commander's color identity.

{T}: Add {C}.
{T}: Untap target legendary creature you control. Activate only once each turn.

{T}: Add {G} or {W}. You lose 1 life unless you have less life than an opponent.

{T}: Add {C}.
{T}: Put a +1/+1 counter on each legendary creature and a loyalty counter on each planeswalker that you control entered this turn.

{T}: Add {C}.
{T}, Sacrifice a Clue: Draw a card.

You may play Coralight Castle from your graveyard as long as seven or more cards are in your graveyard.
Coralight Castle enters tapped.
{T}: Add {W} or {U}.
Cycling {1}{W}{U} ({1}{W}{U}, Discard this card: Draw a card.)

Flying
When Cormoran, Raven Monarch enters, you may put target creature card with mana value 3 or less from a graveyard onto the battlefield under your control.

({T}: Add {B}.)
Corpsebed enters tapped.
When Corpsebed enters, exile up to two target cards from graveyards.

(Transform this if it's not attached to a creature. Pay {3}{B} as a sorcery to unattach it.)
Enchant creature you control
Corrupted Mount's rider gets +5/+4 and can't block.

When Cosmic Contraption enters or leaves the battlefield, you may reveal a noncreature card you own from outside the game and put it into your hand.

As Coveted Tower enters, you may pay 3 life. If you don't, it enters tapped.
{T}: Add {G}, {U}, or {R}.