msem-instigator

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
Hexproof
At the beginning of your upkeep, put a +1/+1 counter on this creature.

Trample
Once each turn, if one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on that creature instead.

Flying
Spirited (When this creature enters, you may activate one of its activated abilities without paying its cost.)
{3}{R}{R}, {T}: Exile an instant card with mana value 3 or less from your graveyard, then cast a copy of a card exiled with Thunderlash Mystic without paying its mana cost.

Flash
Whenever Thundermane Fox enters or attacks, target creature you control gains double strike until end of turn.

Flash
Cycling {2} ({2}, Discard this card: Draw a card.)

When Thunderwhirl Dancer enters, it gets +X/+X until end of turn, where X is the number of +1/+1 counters among creatures you control. Then it fights up to one target creature.

Flash
Menagerie — When Tidal Trickster enters, if there are five or more creature types among creatures you control, you may search your library for a card named Tidal Trickster, reveal it, put it into your hand, then shuffle.

Whenever Tide Crasher attacks, if you control another Merfolk, tap target creature defending player controls.

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)
When Tidepool Turtle has three or more +1/+1 counters on it, remove them all and transform it.

Vanishing 4 (This creature enters with four time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
Remove a time counter from Tideshift Elemental: You may tap or untap target creature.

Double strike (This creature deals both first-strike and regular combat damage.)
If three or more creatures are attacking you, you may cast Timely Commander as though it had flash.

Flying, lifelink
When Timestream Sentinel enters, put two +1/+1 counters on each other creature named Timestream Sentinel you control.

Whenever a creature you control enters, Timid Thunderhorn gets +X/+X until end of turn, where X is that creature's power.

This spell has flash as long as you control a Soldier.
When Tinyvale Watchkeep enters, untap target creature.

First strike
Noncreature spells with mana value 4 or greater cost {1} more to cast.

Chosen one ({W}{U}{B}{R}{G}: Transform this permanent.)
When Tomb Steward enters, search your library for a card and put it into your graveyard. Then shuffle.

When Tomb-Raider Duo enters, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)
Satrapycycling {2} ({2}, Discard this card: Search your library for a Satrapy card, reveal it, put it into your hand, then shuffle.)

When Tombstone Looter enters, you may draw a card. If you do, discard a card.
Unearth {1}{U} ({1}{U}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the end step or if it would leave the battlefield. Unearth only as a sorcery.)

{G}, {T}: Add one mana of any color. When a creature enters this turn, if that mana was spent to cast it, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Tortle Traveler enters tapped.
When Tortle Traveler enters, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Haste
Whenever Tortle Waymaker becomes blocked, 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}{W}, Sacrifice Town Elder: Return target artifact or enchantment card from your graveyard to your hand.

Vision (Whenever this or another creature you control enters, reveal the top card of your library. Then you may put that card into your graveyard.)
Whenever Tracker of Wild Places envisions a creature card, you may untap a permanent you control.

Rapport — Whenever Trae, Serpent's Grasp and at least one other creature you control become tapped, each player draws a card. Then Trae, Serpent's Grasp deals 2 damage to each opponent with four or more cards in hand.