msem-instigator

At the beginning of combat on your turn, target creature you control gets +1/+0 until end of turn. If you cast two or more spells this turn, it also gains haste and trample until end of turn. If you cast three or more spells this turn, it gets an additional +2/+0 until end of turn.

As Ritual Preparations enters, choose a color.
You don't lose unspent mana of the chosen color as steps and phases end.

When River Miscreants enters, target creature you control can't be blocked this turn.
{2}{U}: Return River Miscreants to its owner's hand. Activate only as a sorcery.

Flash
Enchant creature
When Roar of the Wilds enters, enchanted creature gets +3/+3 until end of turn.
When enchanted creature dies, create a 1/1 green Saproling creature token.

When Rotting Greatwurm dies, put three +1/+1 counters on target creature you control.
Fleeting {2}{G} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

Rousing Path enters tapped unless you control one or fewer other lands.
{T}: Add {U} or {R}.
Cycling {2} ({2}, Discard this card: Draw a card.)

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.

[+1]: Tap target permanent. Put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)
[0]: Put target artifact, instant, or sorcery card from your graveyard on top of your library. If you have an insight counter, you may return that card to your hand instead.
[0]: You get an insight counter.
[–1]: Target creature can't be blocked this turn. Until end of turn, whenever that creature deals damage to an opponent, you draw a card.

When Ruins Entrance enters, exile up to three target cards from graveyards.
{1}, {T}: Exile target card from a graveyard.
{5}, {T}, Sacrifice Ruins Entrance: Return target card from your graveyard to your hand.

Defender, flying
Ruins Guardian can attack as though it didn't have defender as long as a creature died under your control this turn.
Whenever Ruins Guardian attacks, you may exile two creature cards from your graveyard. If you do, draw a card.

Ruins Pack gets +2/+2 as long as you sacrificed a permanent this turn.

At the beginning of your end step, Run & Gun deals damage to each opponent equal to the number of tapped creatures you control.

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}.

{T}: You gain 1 life.
{1}{W}, {T}: Tap or untap another target creature.

Prowess, haste
You may spend mana as though it were mana of any color to cast noncreature spells with mana value 3 or less.

When Screams from the Deep enters, exile up to one target monocolored permanent.
As long as an opponent owns three or more cards in exile, you may have Screams from the Deep assign its combat damage as though it weren't blocked.
Evoke {5} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

{T}: Add {C}.
{T}, Tap an untapped artifact, creature, or land you control: Add one mana of any color.
{T}: Choose a card name, then reveal the top card of your library. If that card has the chosen name, you may sacrifice Sealed Archives and draw a card.

At the beginning of your upkeep, surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)
{2}{U}{U}, Sacrifice Search for a New Land: Draw two cards.

Draw three cards. Then discard two cards unless you discard a land card.

Flying, vigilance
Whenever Sepulchral Guide attacks, prevent all combat damage that would be dealt to another target creature you control this turn. If that creature has two or more counters on it, untap it.

Create a 1/1 colorless Human creature token. Put your choice of a flying, vigilance, prowess, or hexproof counter on it. If you control a permanent with mana value 5 or greater, instead put any number of those counters and a +1/+1 counter on it.

Prowess
{1}: Shifting Dweller gets +1/-1 until end of turn.

Shroudmaker's Domain enters tapped.
{T}: Add {W}.

Whenever you attack, each opponent loses 3 life unless they discard a card or sacrifice a nonland permanent. Repeat this process once.
Fleeting {B}{R} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

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.