msem-instigator

When Grievous Buccaneer enters, it voyages. (If it isn't blocking or targeted by another spell or ability, it phases out.)
Whenever Grievous Buccaneer phases in, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Griffin Country enters with a feather counter on it.
Creatures with flying you control get +1/+1.
{U}, Remove a feather counter from Griffin Country: Put a flying counter on target creature you control.
{2}{U}, Remove a feather counter from Griffin Country: Search your library for a creature card with flying, reveal it, put it into your hand, then shuffle.

Flying (This creature can't be blocked except by creatures with flying or reach.)
When Griffin Skycaller enters, target creature you control gets +1/+1 and gains flying until end of turn.

Flying, lifelink

As an additional cost to cast this spell, tap an untapped artifact or creature you control.
Up to three target creatures can't block this turn.

Whenever a creature dies, put a +1/+1 counter on Grim Armory.
Whenever a creature you control enters, you may move a +1/+1 counter from Grim Armory onto it.

As Grim Bastion enters, you may pay 2 life. If you don't, Grim Bastion enters tapped.
{T}, Sacrifice Grim Bastion: Search your library for a Swamp or Forest card, put it onto the battlefield, then shuffle.

When Grim Botanist enters, create a 1/1 green Saproling creature token.
Whenever a nontoken creature you control dies, populate. (Create a token that's a copy of a creature token you control.)

Destroy target creature or planeswalker. Create a Treasure token.

{T}, Sacrifice Grim Courtyard: Search your library for a Swamp or Forest card and put it onto the battlefield tapped, then shuffle.

When Grim Festivities enters or at beginning of your upkeep, you may return a creature card from your graveyard to the battlefield under your control. If you do, each opponent may return a creature card from their graveyard to their hand.

Whenever another Citizen you control dies, you gain 2 life.
{2}{B}, Exile a Citizen card from your graveyard: Each opponent loses 2 life.

{B}, {T}, Exile two cards from your graveyard: Create a 1/1 white Spirit creature token with flying.

When Grim Procession enters, create two 2/2 black Zombie creature tokens.
{2}{B}: Surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)

Target player sacrifices a creature. Create a tapped 2/2 black Zombie creature token.

Equipped creature gets +1/+0 and has wither. (It deals damage to creatures in the form of -1/-1 counters.)
Equip {2}

{T}, Pay 1 life: Add {B} or {R}.
{1}, {T}, Sacrifice Grim Slums: Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Whenever another nonland creature you control dies, return it to the battlefield tapped with a sapling counter on it. It becomes an Animus land named Bitter Hazel, loses all other card types, and gains “{T}: Add {G}” and “Pay this card's mana cost: This land becomes a creature until end of turn. It's still a land.”

{2}, {T}: Create a Treasure token. (It's an artifact with “{T}, Sacrifice this permanent: Add one mana of any color.”)
{W}{U}{B}{R}{G}, {T}, Sacrifice Grim's Warchest: Exile target creature.

Flash
Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
When Grim enters, if you sacrificed a permanent this turn, exile target tapped creature.

Whenever Grin, Scourge of Goresand attacks, when you next cast an instant or sorcery spell with mana value 3 or less this turn, copy that spell. You may choose new targets for the copy.
Dash {2}{R} (You may cast this spell for its dash cost. If you do, it gains haste, and it's returned from the battlefield to its owner's hand at the beginning of the next end step.)

Enchant creature
Enchanted creature has experience. (Whenever it attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)

Sacrifice another creature: Grindlesnap gets +3/+2 and gains trample until end of turn if that creature was a Crocodile. Otherwise, it gets +1/+1 until end of turn.
Whenever Grindlesnap is dealt combat damage, create a 3/2 green Crocodile creature token with trample.

Rapport — Whenever Grinning Fox and at least one other creature you control become tapped, tap another target creature. That creature doesn't untap during its controller's next untap step.

Deception {2}{B} ({2}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Grinning Torturer deals combat damage to a player, torment that player. (They lose 3 life unless they discard a card or sacrifice a nonland permanent.)