msem-instigator

Attacking creatures get +2/+0 and gain trample until end of turn.

At the beginning of combat on your turn, create a 1/1 blue and red Pirate creature token with haste. That token attacks this combat if able.
Whenever Intrepid Captain attacks, other attacking Pirates you control get +1/+0 until end of turn.

Advance {4}{R} (Cast this for {4}{R} to advance it as it enters. {4}{R}: Advance this as a sorcery.)
Whenever Intruder Drone advances, exile the top card of your library. You may cast a spell exiled with Intruder Drone with mana value 3 or less without paying its mana cost.

Inversion of Flesh deals 5 damage to each creature and each planeswalker, and 5 damage to each player with the highest life total or tied for highest life total among players.

Gain control of target creature until end of turn. Put a +1/+1 counter on it and another target creature you control and untap them. Those creatures gains haste until end of turn.

When Ion Field enters, target player creates two 1/1 red Elemental creature tokens.
Whenever you cast an instant or sorcery spell that targets only one target, you may pay {1}{R}{R} and sacrifice Ion Field. If you do, copy that spell for each other target it could target. Each copy targets a different one of those targets.

Other Vampires you control get +1/+1.
Whenever Irascible Bloodwitch or another Vampire enters under your control, Irascible Bloodwitch deals 1 damage to any target.

Choose one —
• Ire of Ancient Tomes deals 2 damage to any target.
• Target instant or sorcery card in your graveyard gains flashback until end of turn. The flashback cost is equal to its mana cost.

Target creature you control deals damage equal to its power to another target creature.
Agonize (You may cast this card from your graveyard by putting a -1/-1 counter on a creature you control in addition to paying its other costs. Then exile this card.)

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.)

Trample
At the beginning of each combat, you may have Ironhide Bellower deal 3 damage to target creature you control. If you do, Ironhide Bellower gets +3/+0 and can't be blocked by creatures with total power 3 or less until end of turn.

Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)

Embellish {3}{R}{R} (If you cast this spell for {3}{R}{R}, create a 1/1 blue Thopter artifact creature token with flying when it enters.)
Desecrate (When this creature enters, you may sacrifice an artifact or land.)
When Ironsmash Drill-Delver desecrates a permanent, it deals 3 damage to any target.

When Ironsmash Wrecker enters, you may destroy target artifact.

Flying, haste
Dominance — At the beginning of combat on your turn, if you control the creature with the greatest power or tied for the greatest power, you may pay {1}{R}. If you do, return Issbarren Phoenix from your graveyard to the battlefield.

Haste (This creature can attack and {T} as soon as it comes under your control.)

Menace (This creature can't be blocked except by two or more creatures.)
Itava Warshrieker attacks each combat if able.

Art of war — At the beginning of your end step, if Jaakuna Betrayer dealt damage to an opponent this turn, you may discard a card. If you do, draw a card.

When Jaakuna Bloodsworn enters, any opponent may have it deal 3 damage to them. If a player does, sacrifice Jaakuna Bloodsworn.

Double strike
Art of war — At the beginning of your end step, if Jaakuna Tyrant dealt damage to an opponent this turn, put a +1/+1 counter on it.

As long as Jadycian Empath is on the battlefield or in your graveyard, it's a land in addition to its other types.
Sacrifice Jadycian Empath: Add one mana of any color.

Whenever Jak, Daring Vanguard or another legendary creature you control enters, creatures you control get +1/+0 and gain haste until end of turn.

Lionize {2}{R} ({2}{R}, Exile this card from your hand: Put a +1/+1 counter on target creature and it gains the following abilities until end of turn. You may cast this card on a later turn from exile.)
Double strike

Menace
Inspired — Whenever Jeering Kit becomes untapped, target Fox you control gets +1/+1 until end of turn.