msem-instigator

Flying
When Rapacious Regent enters, you may sacrifice another creature or artifact. If you do, Rapacious Regent deals 3 damage to any target.

At the beginning of combat on each of your turns, you may sacrifice a land or exile a land card from your graveyard. If you do, create two 1/1 red Goblin creature tokens with haste. Exile those tokens at the beginning of the next end step.

If a player taps a nonbasic land for mana, that land produces {C} instead of any other type.
Whenever Rylei Wakebreaker attacks, it and another target creature you control each get +1/+0 until end of turn for each attacking creature you control.

When Sandmouth Dragon enters, another target creature you control gets +3/+0 until end of turn.
Mirage {2}{R} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

Flying
Tap five untapped Satrapies you control: Untap all creatures you control. After this main phase, there is an additional combat phase followed by an additional main phase. Activate only as a sorcery.

Whenever you cast a spell, if mana from an artifact was spent to cast it, exile the top card of your library. You may play that card until you exile another card with Savant of Cables.

First strike
Disgraced 1 (This enters with a -1/-1 counter. Whenever it deals combat damage to a player, remove all -1/-1 counters from it.)

Trample, prowess

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you casting a noncreature spell causes an ability of a creature you control to trigger, that creature gains your choice of first strike, haste, menace, or trample until end of turn.

Improve {1}{R} ({1}{R}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
When Siegebreaker Ogre enters, create two 1/1 red Goblin creature tokens with haste.

First strike

Menace
Whenever Skhorvall Warleader attacks, it gets +1/+0 until end of turn for each other attacking Warrior you control.

Haste, prowess
Wanderlust — When Spitfireling enters, if you control four or more differently named lands, create two 1/1 red Elemental creature tokens with prowess and haste.

If you would draw a card, you may skip that draw. If you do, create a tapped Treasure token and exile the top card of your library. You may play that card this turn.

When Sunset Cliffs Lawman enters, you may post a bounty on target creature. (Put a bounty counter on that creature. It has “When this creature dies, each opponent draws a card” as long as it has a bounty counter on it.)

Haste
Whenever The Marquess Devonport attacks, it deals 2 damage to you.
Attain {5}{R} ({5}{R}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

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

Vanguard — Whenever a creature you control attacks alone, it gets +1/+1 and gains menace until end of turn.

When Timecrafter Lafterii enters, choose target permanent with one or more time counters on it, then put two time counters on it or remove two time counters from it.

Haste
When Treasure Haulers enters, you may salvage an artifact card. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)

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

Undine Coven gets +1/+1 for each other Merfolk you control.
Whenever you cast a noncreature spell, Undine Coven deals 1 damage to target player or planeswalker.

Whenever another creature you control dies, creatures you control get +1/+0 until end of turn.
Whenever this creature attacks, you may pay {2}{R} and sacrifice another creature. If you do, this creature gains menace until end of turn.

When Viashino Glutton enters, you may have it consume. If you do, create two 1/1 red Goblin creature tokens. (To consume, sacrifice another creature or exile a creature card from your graveyard.)

Flying, haste
Whenever Vidal's Conjurant attacks, reveal the top six cards of your library. You may put an enchantment card with mana value 3 or less from among them onto the battlefield. If you do, sacrifice that enchantment at the beginning of the next end step. Put the rest on the bottom of your library in a random order.