msem-instigator

Mill a card. Target creature gets -X/-X until end of turn, where X is the number of cards put into your graveyard from anywhere this turn.

Ward {1}
Other Scouts you control get +1/+1.
Whenever three or more Scouts you control attack, draw a card.

Indestructible
Marva of Endless Inspiration can't attack or block unless you've cast a spell with mana value 4 or greater this turn.
At the beginning of your end step, return a card at random from your graveyard to your hand. If it's a land card, return it to the battlefield instead.

First strike, trample
Whenever Regal Coralhorn deals combat damage to a player or planeswalker, return target card with a cycling ability from your graveyard to your hand.
Cycling {2} ({2}, Discard this card: Draw a card.)

{T}: Add {C}.
{3}, Exile Resurgent Oasis from your graveyard: Choose a basic land type. Create a tapped colorless land token that's a Desert and the chosen basic land type.

Enchant creature
Enchanted creature gets +0/+1 and has hexproof.
Mirage {U} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

Whenever Paomar Greatheart attacks, put a trample counter on target attacking creature in its pack. (Two or more creatures you control with equal power are in a pack.)

Whenever a land you control enters, if you haven't had a land become a copy this way this turn, you may have that land enter as a copy of any nonland permanent on the battlefield.

When Frontier Scouts enters, reveal the top card of your library. If it's a land, put it onto the battlefield tapped.

When Architect of the Derezzed enters, create two 1/1 colorless Servo artifact creature tokens.
Sacrifice an artifact: Target creature can't be blocked this turn.

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}: If you control ten or more nonland permanents, unlock Riddle of Entropy.
As long as the revealed card is a permanent card, each nonland permanent you own is a copy of it.

At the beginning of combat on your turn, you may have target artifact you control become a 3/3 artifact creature until end of turn. If you do, it and Field Engineer attack this turn if able.

Vigilance
Whenever a creature you control survives damage, it explores. (Reveal the top card of your library. Put it into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then you may put that card in your graveyard.)

[+1]: Scry 1. Untap up to one target creature.
[–2]: Mill a card for each card type among permanents you control, then you may return a land card and/or a nonland card milled this way to their owner's hand.
[–6]: Until end of turn, you may cast spells from your hand and graveyard without paying their mana costs. If a card would be put into your graveyard from anywhere this turn, exile it instead.

Flash

Look at target player's hand. That player discards a card.
{2}{B}{B}, Exile Psychic Assault from your graveyard: Choose a card name. Target player reveals their hand and discards all cards with that name. Activate only as a sorcery.

Whenever one or more counters are put on a permanent you control for the first time each turn, create that many 1/1 green Squirrel creature tokens.
{1}{G}{W}, {T}: Proliferate. (Choose any number of permanents and/or players with counters on them, then give each another counter of each kind already there.)

Exile up to three target cards from a single graveyard. Create a tapped 2/2 colorless Spirit creature token.

Whenever another creature you control enters, you may change Reshaping Primordial's base power and toughness to that creature's power and toughness.

Look at the top two cards of your library. You may put both of those cards into your graveyard or back on top of your library in any order.
Draw a card.

Target creature gets -4/-4 until end of turn.
Civilized — Draw a card if you control an artifact, a creature, and an enchantment.

{T}: Add {C}.
{T}, Pay 1 life: Add {W}.
{5}{W}, {T}, Sacrifice Swaying Sands: Create three 1/1 white Bird creature tokens with flying. Activate only as a sorcery.

Whenever another nontoken creature you control dies, you may return it to the battlefield tapped face down under its owner's control. It's a Forest land.
{4}{G}, Return a land you control to its owner's hand: Create a 3/3 green Wurm creature token. Activate only as a sorcery.

Siphon (Each -1/-1 counter you put on your creatures up to their remaining toughness while casting this pays for {1}.)
Costly Ambush deals damage equal to the greatest power among creatures you control to target creature or planeswalker.

Trample