msem-instigator

Equipped creature gets +1/+0 and can't be blocked.
Equip Actor creature {1}
Equip {3}

{2}{R}: Thespian Soldier gains first strike until end of turn.

Trample
Stampede — Whenever Thoctar Yearling and a creature with greater power attack, put a +1/+1 counter on Thoctar Yearling.

{T}: Add {G}. If there are three or more creature cards in your graveyard, add {G}{G} instead.

Reach, deathtouch

Prismatic — Whenever you cast a multicolored spell, Thorny Bushwacker has base power and toughness 5/3 until end of turn.

Purge, then you may pay 2 life. If you do, purge again. (To purge, exile two cards that share a type from graveyards. If you do, draw a card.)

(Choose only one work as a sorcery to add its ability.)
When Those Lost to the Waves enters, search your library for an artifact card with mana value 3 or less, reveal it, put it into your hand, then shuffle.
{1}{W}: Fight the Current
Equipped creatures you control get +1/+1.
{3}{U}: Soul of the Sea
At the beginning of combat on your turn, you may have target noncreature artifact become a 3/3 artifact creature until end of turn.

Counter target instant or sorcery spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard. You may cast that spell for as long as it remains exiled and you may spend blue and black mana as though it were mana of any color to cast it.

When Thought Paradigm enters, conjure a card named Data-Point into your hand. (It's a sorcery that costs {2} with “Draw a card.”)
Whenever you cast a sorcery spell, target player mills three cards.

When Thoughtslick Engineer enters, each player discards a card at random.

Target creature gets +1/+1 until end of turn for each creature you control.
Inscribe {3}{R} ({3}{R}: Exile this card from your hand inscribed on a creature you control. Whenever that creature attacks, its controller may cast a copy of the inscribed card without paying its mana cost. Inscribe only as a sorcery.)

This spell costs {2} more to cast for each target beyond the first.
Choose one or more —
• Counter target creature or planeswalker spell with mana value 4 or less.
• Exile target permanent you control, then return that card to the battlefield under your control.
• Target player draws two cards, then discards two cards and mills two cards.

Flash
When Threadripper Savant enters, put a stun counter on up to one target creature.

Menace (This creature can't be blocked except by two or more creatures.)

Enchant creature
Enchanted creature gets +3/+1.

When Three Seas Squire enters, target creature or Vehicle gets +2/+1 until end of turn.

As an additional cost to cast this spell, discard a card.
Draw two cards.

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.

Target player mills three cards for each poison counter they have.

The next creature spell you cast this turn may be cast as though it had flash and costs {1} less to cast. If it entering the battlefield causes a triggered ability of it to trigger, that ability triggers an additional time.

You may sacrifice a land. If you do, search your library for a land card, put that card onto the battlefield, then shuffle.
Inscribe {3}{G} ({3}{G}: Exile this card from your hand inscribed on a creature you control. Whenever that creature attacks, its controller may cast a copy of the inscribed card without paying its mana cost. Inscribe only as a sorcery.)

Target creature gets +1/+1 for each creature you control and gains flying and vigilance until end of turn.

Thunderous Applause deals damage to any target equal to the number of tapped creatures you control.

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.