msem-instigator

When Cosmonaut Pioneer enters or leaves the battlefield, choose one—
• Scry 1, then draw a card.
• Create a 3/3 green Alien creature token with trample.
• You gain 5 life.

Erratic (When this creature dies, reveal the top four cards of your library. Put a creature card that costs less than this revealed this way onto the battlefield and the rest on the bottom of your library in any order.)
Whenever a creature you control enters, if you didn't cast it from your hand, target land you control becomes a 7/1 red Elemental creature with trample and haste. It's still a land.

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)
Flying
{2}{W}: Prevent all damage that would be dealt to and dealt by creatures with counters on them this turn.

When Cou Ling enters, create two 2/1 red and white Fox creature tokens.
Whenever a Fox you control deals combat damage to a player, draw a card, then you may cast an instant or sorcery card with mana value less than or equal to the damage dealt from your hand without paying its mana cost.

Sacrifice a creature: Each opponent loses 1 life and you gain 1 life.
Sacrifice two creatures: Draw a card.
Sacrifice three creatures: Exile target creature or planeswalker.

Flying
Whenever a creature you control that isn't enchanted dies, adjudicate.
Whenever an enchanted creature you control dies, return it to the battlefield at the beginning of the next end step.

As an additional cost to cast this spell, tap an untapped Warlock you control.
Search your library for a card and put it into your hand or graveyard, then shuffle.

Target opponent chooses a card type, then reveals their hand. You choose a card from it that's not of the chosen type. That player discards that card.

Equipped creature gets +2/+1.
Whenever equipped creature becomes the target of a spell or ability for the first time each turn, counter that spell or ability.
Equip {2}

Enchant creature
Enchanted creature gets +2/+2 and has “Whenever this creature attacks, tap target creature defending player controls.”

Gain control of target artifact or creature until end of turn, then untap it. It gains haste until end of turn. You may spend mana as though it were mana of any type to pay the costs of its abilities this turn.

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

Choose two —
• Destroy target artifact.
• Discard a card, then draw a card.
• Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

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.

{3}, {T}: You may put an artifact card with mana value 3 or less from your hand onto the battlefield. This ability costs {1} less to activate for each other artifact you control.

This spell costs {X} less to cast, where X is 20 minus your life total.
First strike, menace, trample

Prowess
When Cramming Student enters, conjure ten cards named Fatigue and shuffle them into your library. (They're colorless sorceries that cost {2} and have “Draw a card.”)
Instant and sorcery spells you cast cost {1} less to cast.

Once each turn, you may reveal a creature card as you draw it. Whenever you do, create a 1/1 green and blue Bird creature token with flying and “{T}: Add one mana of any color.”
Whenever three or more creatures you control deal combat damage to a player, untap each creature you control.

Flash
When Cranial Glass enters, exile target card from a graveyard.
{7}, {T}, Sacrifice Cranial Glass: Copy the exiled card. You may cast the copy without paying its mana cost. (A copy of a permanent spell becomes a token.)

Trample, haste
All creatures able to block Crashing Mammoth do so.

As an additional cost to cast this spell, discard a nonland card.
Draw two cards.

Bloodprice—Reappropriate red. (You may cast this spell by sacrificing a creature and exiling two red cards from your hand and/or graveyard.)
Haste
Whenever Creed's Desperado attacks, if defending player has more cards in hand than you, exile the top card of that player's library. You may cast it as long as you control a Warrior, and you may spend mana as though it were mana of any color to cast it.

First strike
Whenever Creed, Eternal Straggler attacks, exile the top card of your library. You may play that card this turn, and that spell costs {2} less to cast.

When Crescent of the Harvest Moon enters or whenever equipped creature attacks, exile up to one target card from a graveyard.
Equipped creature gets +1/+1.
{X}: Equipped creature becomes a copy of a permanent card with mana value X or less exiled with Crescent of the Harvest Moon until end of turn (even if this becomes unattached). Activate only as a sorcery.
Equip {2}

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.