msem-instigator

When Gemcrusher Turtle enters the battlefield, choose one —
• Destroy target artifact.
• Gemcrusher Turtle fights up to one target creature.

Flying, haste
Whenever one or more other nontoken Pirates and/or Rogues you control attack, create a 1/1 red Pirate creature token.

({T}: Add {U} or {B}.)
Ghostspore Mire enters the battlefield tapped.
{1}, {T}: Add {U}{U} or {B}{B}.

When Gilded Merrow enters the battlefield, if an opponent controls more lands than you, create a Treasure token. (It's an artifact with “{T}, Sacrifice this permanent: Add one mana of any color.”)

{T}, Discard a card: Draw a card.
Unveil {2}{U}{R} ({2}{U}{R}: Transform this. Unveil only as a sorcery.)

{G}{U}: Glacier Tortoise gets +5/-5 until end of turn. Activate only once each turn.

Vigilance
Whenever Glittering Narwhal is dealt damage, create a Treasure token. (It's an artifact with “{T}, Sacrifice this permanent: Add one mana of any color.”)

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
Cycling {B} ({B}, Discard this card: Draw a card.)

When Glowskate Channeler enters the battlefield, create a green Aura enchantment token named Manta's Wings attached to target creature. The token has enchant creature and “Enchanted creature gets +2/+2.”

Whenever you cycle a card, reveal the top two cards of your library. You may put a permanent card from among them into your hand. Put the rest on top of your library in any order or into your graveyard.
Cycling {2} ({2}, Discard this card: Draw a card.)

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Whenever Goldtooth Slasher attacks, you may sacrifice an artifact or creature. If you do, Goldtooth Slasher gets +2/+0 and gains lifelink until end of turn.

Whenever Goreswimmers deals combat damage, put a +1/+1 counter on Goreswimmers.

When Greedy Rapscallions enters the battlefield, mill three cards. If two or more nonland cards were put into your graveyard this way, put a +1/+1 counter on Greedy Rapscallions.

Whenever Greenscale Bully deals combat damage to a player, create a Treasure token. (It's an artifact with “{T}, Sacrifice this permanent: Add one mana of any color.”)

When Grievous Buccaneer enters the battlefield, 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.

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

Resolute — {T}: Grizzled Cutthroat deals 1 damage to any target. Activate only if Grizzled Cutthroat's power is greater than its base power.

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
Gui can't attack or block unless you're in a renaissance.
{T}: Reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put it back on top or into your graveyard and you gain 3 life.

Hexproof, trample
Whenever Gui, the Islandbringer deals combat damage to an opponent, reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put it into your hand.

When Gulchdrinker Serpent enters the battlefield, detain target permanent. (Until your next turn, that permanent can't attack or block and its activated abilities can't be activated.)

Flash
When Guppyfin Duelist enters the battlefield, create a green Aura enchantment token named Piranha's Prowess attached to target creature. The token has enchant creature and “Enchanted creature gets +2/+2.” Untap that creature.

At the beginning of combat on your turn, for each permanent type, aetherize up to one target permanent you control of that type. (To aetherize, create a token that's a copy of it, then exile that token.)

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Whenever Happy Manta deals combat damage to a player, draw a card for each card type among spells you've cast this turn.

Flying, trample
Harbinger of Falling Skies enters the battlefield with X +1/+1 counters on it.
Whenever Harbinger of Falling Skies attacks, you may remove a +1/+1 counter from it. If you do, draw a card.

{U}, Give yourself a lore counter: Scry 1. This ability costs {2} more to activate for each lore counter you have.
{6}{U}, Remove three lore counters from yourself, Sacrifice Harbinger of Giradrus: Draw seven cards, then create two 4/4 red Dragon creature tokens with flying.