msem-instigator

Treacherous Oasis enters tapped.
{T}: Add {U} or {B}.
{2}{U}{B}: Until end of turn, Treacherous Oasis becomes a Crocodile creature in addition to its other types. It can't be blocked this turn.
Scavenge {1}{U}{B}

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

(Add a quest counter as this enters. Sacrifice after 3.)
Whenever you scry or search your library, add a quest counter.
Target creature you don't control gets -3/-0 until your next turn.
Reveal cards from the top of your library until you reveal a nonland card, then put the revealed cards into your hand.
Reveal the top card of your library. If its mana value is less than or equal to the number of cards in your hand, you may cast it without paying its mana cost.

As Tree of Timelines enters, you may pay 3 life. If you don't, it enters tapped.
{T}: Add {B}, {G}, or {U}.

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever a +1/+1 counter is put on Treecrawler Elemental, you may have it fight target creature. (Each deals damage equal to its power to the other.)

When Trenchbottom Mariners enters, you lose 3 life, mill three cards, and create a Treasure token.
Whenever Trenchbottom Mariners attacks, you may cast a permanent card from your graveyard by sacrificing another artifact in addition to paying its costs.

This spell costs {1} less to cast for each card you've drawn this turn.
Create three 1/1 white Soldier creature tokens.

When Trident of Benediction enters, create two 1/1 white Merfolk creature tokens.
Equipped creature has vigilance and “Whenever this creature attacks or blocks, creatures you control get +1/+1 until end of turn.”
Equip {2}

Erratic, erratic, erratic (When this creature dies, reveal the top four cards of your library. Put a creature card that costs less than this revealed this way onto the battlefield and the rest on the bottom of your library in any order. Repeat this process twice.)

Whenever an opponent casts their first spell each turn, that player may pay {1}. If they don't, you may create a Treasure token and you may draw a card.

Copy target spell twice. You may choose new targets for the copies. (A copy of a permanent spell enters as a token.)

If you would put one or more counters on a creature you control or on yourself, put that many plus one of each of those kinds of counters on that creature or player instead.
{2}{G}{U}, Sacrifice Triton's Invocation: Draw cards equal to the greatest number of counters among creatures you control and yourself.

Creatures you control gain double strike until end of turn. Whenever a creature you control deals combat damage this turn, put a +1/+1 counter on it.

Rhapsody {4}{U}{U} (Pay {4}{U}{U} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
Whenever you cast a noncreature spell, Triumvirate Inductee gets +1/+1 until end of turn. Then if its power is 4 or greater, you may tap or untap target permanent.

{T}, Pay 1 life: Add {G}.
{T}, Pay 1 life, Sacrifice Tropical Grove: Search your library for a Forest card, put it onto the battlefield tapped, then shuffle.

Once each turn, when you search your library, you may add {B}{B}.

Flying
When Trove Tyrant enters, exile the top five cards of your library.
Whenever Trove Tyrant deals combat damage to a player, you may cast an artifact card exiled with it without paying its mana cost.

Exile target creature. Its controller reveals cards from the top of their library until they reveal a creature card. The player puts that card onto the battlefield, then shuffles all other cards revealed this way into their library.

Activated abilities of creatures you control cost up to {1} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Flash
When Tsang Jin, Master of the Jade Sea enters, 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.

Flying
Lands you control have “{T}: Add {R}{R}. This land deals 2 damage to you.”
{R}{R}{R}{R}{R}{R}: Shuffle your library, then exile the top three cards. You may cast one of them without paying its mana cost.

Trample, hexproof
Renown 4 (When this creature deals combat damage to a player, if it isn't renowned, put four +1/+1 counters on it and it becomes renowned.)
{1}{G}: Target creature blocks Tsolmon, the Huntress this turn if able.

Hexproof
Whenever this creature transforms into Tsunami Titan or attacks, you may return target creature to its owner's hand.

At the beginning of your end step, draw a card if a creature died this turn. Then Tumultipede deals 2 damage to each opponent if two or more creatures died this turn. Then create three 1/1 green Saproling creature tokens if three or more creatures died this turn.