msem-instigator

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.)

Vigilance, reach
When Treeline Archer enters, mill four cards.
{5}{G}: Transform Treeline Archer. Activate only if it's attacking.

Flash (You may cast this spell any time you could cast an instant.)
Reach (This creature can block creatures with flying.)

Prevent all combat damage creatures with flying would deal this turn. Creatures you control gain reach until end of turn.

Whenever Tremor Elemental enters or you draw a card except during your draw step, Tremor Elemental deals 1 damage to each creature.

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

Whenever Tremor Titan enters or attacks, each player sacrifices a permanent. Then you draw a card for each opponent who sacrificed a land this way.

Whenever a land you control enters, put a +1/+1 counter on target creature you control.

When Trepid Deserters enters, target creature you control gets +2/+0 until end of turn.

I — Create a 1/1 red Hound creature token.
II — Create a 4/4 green Rhino Warrior creature token with trample.
III — You may have two target creatures you control fight. If you do and exactly one survives, put four +1/+1 counters on that creature.

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.

Equipped creature has menace.
Whenever equipped creature attacks, look at the top two cards of your library. Put any number of them into your graveyard and the rest back on top of your library in any order.
Equip {2}

{4}{G}{G}, Exile six other cards from your graveyard: Return Trifold Atrocity from your graveyard to the battlefield with three +1/+1 counters on it. Activate only as a sorcery.

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

As an additional cost to cast this spell, discard a land card.
Exile the top two cards of your library. Until end of turn, you may play those cards.

Pressure {1}{G}{G} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Trample
Whenever Triplicate Monstrosity deals combat damage to a player, draw a card.

Triumphant Return deals 3 damage to up to one target creature. You may put an exiled creature card you own that's on an Adventure into your hand.

Rhapsody {4}{R}{R} (Pay {4}{R}{R} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
Double strike

{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.

When Troubled Heir dies, create a tapped Plains token.

When Troubled Homesteader dies, draw a card.

Menace
{3}{R}: Transform Troublesome Throng. Activate only if it's attacking.

Flying
When Trove Keeper dies, create two Treasure tokens.