msem-instigator

Vision (Whenever this or another creature enters the battlefield under your control, 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.

Flash
When Trade Route Bandit enters the battlefield, you may have each player draw two cards.

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.

When Transcended Explorer enters the battlefield, if you control another enchantment, draw a card.

Wanderlust — When Transnaturalist enters the battlefield, if you control four or more differently named lands, you may return target creature to its owner's hand.

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)
{1}{W}, Sacrifice a creature or enchantment: Scry 1, then draw a card. Activate only if Trauma Surgeon has a +1/+1 counter on it.

Trial 4 (As you cast this spell, an opponent of your choice may pay 4 life. If they don't, they fail the trial.)
When Treacherous Devil enters the battlefield, if an opponent passed the trial, that player gains control of Treacherous Devil.

When Treacherous Warden enters the battlefield, search your library for a card, put into your graveyard, then shuffle.
Whenever a creature enters the battlefield from your graveyard, each opponent loses 2 life and you gain 2 life.

Whenever another nontoken creature enters the battlefield under your control, that creature gains haste until end of turn. Then Tremor Seer deals 1 damage to any target.

Goblincycling {1}{R}, Warriorcycling {1}{R} ({1}{R}, Discard this card: Search your library for a Goblin or Warrior card, reveal it, and put it into your hand. Then shuffle.)

Trample
Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
Whenever Tribal Guard mentors a creature, that creature gains trample until end of turn.

{G}, {T}: Target creature with power 4 or greater fights any number of target creatures you control.

Triumvirate Infiltrator has flying as long as you control another Elemental.

Rhapsody {4}{W}{W} (Pay {4}{W}{W} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
Triumvirate Strategist has first strike as long as it's attacking.

At the beginning of your upkeep, if you control a legendary creature, put a +1/+1 counter on Trossingen Warden.

Flying
When Trove Keeper dies, create two Treasure tokens.

Harmony — Search your library for a basic land or Desert card, reveal it, and put it into your hand. Then shuffle.
When Trumpeting Pathmaker enters the battlefield, harmonize. (Trigger up to one harmony of a permanent you control.)

Vigilance
Assault {G} (Whenever this attacks, if it has no +1/+1 counters on it, you may pay its assault cost to put a +1/+1 counter on it.)

{T}, Mill two cards: Add one mana of any color.

Flash
When Tsang Jin, Master of the Jade Sea enters the battlefield, put target land card from a graveyard onto the battlefield under your control.

Flying
Whenever you tap a Mountain for mana, add {R} and that land deals 1 damage to you.
Whenever you tap a non-Mountain land for mana, that land deals 1 damage to Tseng, Warden of the Peak.

Haste
Whenever Tunnel Moles attacks, you may have it phase out. (Treat it and anything attached to it as though they don't exist until its controller's next turn.)
Whenever Tunnel Moles phases in, it gets +2/+2 until end of turn and can't be blocked by creatures with flying this turn.

Flying, lifelink
Sacrifice a creature: Until end of turn, Turned Watcher gets +1/+0 and gains “Whenever Turned Watcher deals combat damage to a player, draw a card.”

Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)
When Tutorial Boss enters the battlefield, create a 1/1 blue Pirate creature token.

When Twice-Lived Dead dies, create a 2/2 black Zombie creature token.