msem-instigator

When Mouthpiece of Yhzag enters, you may have target opponent create a tapped 1/1 colorless Human creature token.
Whenever Mouthpiece of Yhzag attacks, gain control of target Human creature you don't control with mana value 3 or less until end of turn. Tap it. It's attacking.

At the beginning of your upkeep, Reality Collapse deals 1 damage to each opponent.
{2}{R}: Until end of turn, whenever an opponent is dealt noncombat damage, Reality Collapse deals that much damage to target creature that player controls.

{T}: Target creature gains haste until end of turn.
{1}{R}, {T}, Sacrifice a Human: Create a token that's a copy of the sacrificed creature, except it's a 3/2 colorless Horror. It gains haste until end of turn. Activate only as a sorcery.

If you would draw a card, you may skip that draw. If you do, create a tapped Treasure token and exile the top card of your library. You may play that card this turn.

Flying
{1}{R}{R}{R}: Return Umbral Hunter from your graveyard to your hand. If it's the declare attackers step, up to one target attacking creature gets +3/+1 until end of turn.

Improve {1} ({1}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
Once each turn, when one or more counters are put on a permanent you control, create a 1/1 colorless Human creature token.
Whenever you attack with three or more creatures, destroy up to one target artifact or enchantment.

Reach, vigilance
When Amorphous Tyrant enters, another target creature you control deals damage equal to its power to target creature or planeswalker you don't control.
Evoke {G} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

[+1]: Add two mana of any one color.
[0]: Put two +1/+1 counters on target creature you control. Then put your choice of a reach, vigilance, or trample counter on it. If you have an insight counter, you may put all of those counters on that creature instead.
[0]: You get an insight counter.
[–2]: Destroy target noncreature, nonland permanent.

Improve {1} ({1}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
{T}: Add one mana of any color.
{T}: Add X mana of any one color, where X is the greatest number of counters among creatures you control.

{1}{G}: Return another target permanent you control to its owner's hand.
{X}{G}: You may put a creature card with mana value X or less from your hand onto the battlefield. It gains trample and haste until end of turn.

When Keeper of the Ancient Ways enters, destroy up to three target noncreature, nonland artifacts and/or enchantments with total mana value 3 or less.

When Memories Rewound enters, you may put target card from your graveyard on top of your library.
{1}: Put target card from your graveyard on the bottom of your library. Activate only once during each of your turns.

Molting Abomination can't be blocked by creatures with power 2 or less.
Whenever Molting Abomination deals combat damage to a player or planeswalker, create a tapped 3/2 colorless Horror creature token. Put a stun counter on that token. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Once each turn, when Rova, the Fleshweaver enters or you attack with one or more Horrors, you may put a +1/+1 counter on each creature you control. Then if Rova isn't a token, untap each land you control. Until your next turn, you may cast permanent spells as though they had flash.
{2}{G}{G}, Discard Rova: Create a token that's a copy of Rova, the Fleshweaver, except it's 4/4 and isn't legendary. Activate only as a sorcery.

You may spend mana as though it were mana of any color to cast spells with mana value 5 or greater or to activate abilities of permanents or permanent cards with mana value 5 or greater.
{T}: Add {C}.

Sire of the Shapeless costs {3} less to cast as long as you control three or more creatures.
Trample, haste
{G}, Reveal Sire of the Shapeless from your hand: Create a 1/1 colorless Human creature token. Shuffle Sire of the Shapeless into your library. Activate only as a sorcery.

As Theodore Harper, Head Librarian enters, choose Fact or Fiction.
• Fact — Permanent spells you cast cost {1} less to cast. This effect can't reduce the amount of mana a spell costs to cast to less than one mana.
• Fiction — When Theodore Harper enters, return a permanent card from your graveyard to your hand.

When Vile Progenitor enters, create a 3/2 colorless Horror creature token.
As long as you control five or more lands, Horrors you control get +1/+1 and have trample.
Evoke {1}{G} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Whenever Voracious Spawn enters or attacks, exile up to one target card from a graveyard. If you exile a permanent card, put a +1/+1 counter on Voracious Spawn. If you exile a nonpermanent card, you gain 1 life.

Fleshweaver's Domain enters tapped.
{T}: Add {G}.

Improve {1} ({1}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
Other creatures you control have improve {1}.

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.)

{T}: Put target permanent you own on the bottom of your library.
{1}, {T}: Add one mana of any color. When that mana is spent, target opponent loses 1 life.

When Eternity's Eye enters, look at the top seven cards of your library. Put up to three of them into your graveyard and the rest on the bottom of your library in a random order.
{T}: Add one mana of any color.
{2}: Put target card from a graveyard on the bottom of its owner's library.

Equipped creature has hexproof and improve {1}. ({1}: Put a +1/+1 counter on that creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
{4}: Put Faithforged Pauldron from your hand onto the battlefield attached to target creature.
Equip {1}