msem-instigator

Post a bounty on target creature. (Put a bounty counter on that creature. It has “When it dies, each opponent draws a card” as long as it has a bounty counter on it.)
Draw a card.

Whenever Wasting Soul attacks or blocks, sacrifice a creature, then put two +1/+1 counters on Wasting Soul.

Azun's Play deals damage to any target equal to the number of cards in your hand.
Quickdraw {R}{R} (When a creature you control blocks or becomes blocked, you may cast this spell for {R}{R}.)

Discard a card: Bloodshot Berserker gets +1/-1 until end of turn. Any player may activate this ability.

Haste
Whenever one or more creatures attack, you may discard a card. If you do, draw a card.

Target creature gets +3/+2 and gains menace until end of turn.
Quickdraw {1}{R} (When a creature you control blocks or becomes blocked, you may cast this spell for {1}{R}.)

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

First strike
Whenever Creed, Eternal Straggler attacks, exile the top card of your library. You may play that card this turn, and that spell costs {2} less to cast.

Crossfire deals 1 damage to each creature.
Quickdraw {2}{R} (When a creature you control blocks or becomes blocked, you may cast this spell for {2}{R}.)

When Deputy Gibem enters, post a bounty on each creature and each planeswalker. (Put a bounty counter on those permanents. Each of them have “When this permanent dies, each opponent draws a card” as long as it has a bounty counter on it.)

Exile the top two cards of your library. Until end of turn, you may play cards exiled this way. If an instant or sorcery spell cast this way would deal damage to a player or planeswalker, it deals double that damage instead.

Menace, haste
Other Centaurs you control get +1/+0.

Enchant creature
Enchanted creature has +2/+0 and has haste.
Quickdraw {R} (When a creature you control blocks or becomes blocked, you may cast this spell for {R}.)

[+1]: Haide Bankbuster deals 2 damage divided as you choose among one or two targets.
[+1]: Draw two cards unless any player has Haide Bankbuster deal 3 damage to them.
[–9]: Until end of turn, gain control of all permanents target player controls and they gain haste. Untap those permanents.

Haste
{2}{W}, {T}: Hair-Trigger Marshall deals 2 damage to target blocking creature.

Reach

When Howler Sheriff enters, gain control of up to one target creature with a bounty counter on it until end of turn. Untap that creature. It gains haste until end of turn.

Injustice deals 4 damage to target creature. Post a bounty on up to one other 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.)

When Ironeyes Desperado is exiled from your library, you may pay {R}. If you do, cast it without paying its mana cost.
Haste

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Gain control of target land.

Target creature gains haste until end of turn. Make an Entrance deals 2 damage to up to one target creature.

Until end of turn, target creature gets +2/+2 and gains “Whenever this creature attacks, you may post a bounty on target creature.” (Put a bounty counter on that creature. It has “When it dies, each opponent draws a card” as long as it has a bounty counter on it.)

Whenever Open Road or another permanent you control enters, if it has the greatest mana value among permanents you control, you may discard a card. If you do, draw a card.