msem-instigator

Whenever Inspiring Tactician or another permanent you control becomes the target of a spell or ability you don't control, amass Soldiers 1. (Put a +1/+1 counter on an Army you control. It's also a Soldier. If you don't control one, create an 0/0 black Soldier Army creature token first.)

Inspirited Duelist has double strike as long as it has a +1/+1 counter on it.

Flying
{1}{W}: Exile target artifact you control. Return that card to the battlefield under your control at the beginning of the next end step.

Interan Soothsayer gets +1/+1 for each other green creature you control.
{G}, {T}: Put a +1/+1 counter on target green creature.

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.

Improve {W} ({W}: 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.)
Whenever one or more embattled creatures you control attack, create a 1/1 white Cleric creature token with lifelink. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

When Intrepid Shieldmate enters, target creature gets +1/+1 until end of turn.

Flash
When Intrepid Shooter enters, it deals 2 damage to target attacking creature.

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.

At the beginning of your upkeep, rouse 1. Then if you control a creature with power 5 or greater, put a +1/+1 counter on each creature you control. (Put a +1/+1 counter on a permanent you control. If it isn't a creature, tap it and it becomes a 0/0 creature in addition to its other types.)

Flying (This creature can't be blocked except by creatures with flying or reach.)
When Iridescent Familiar enters, if you control another creature with flying, draw a card.

First strike
Whenever you cast an artifact or enchantment spell, put a +1/+1 counter on Ironclad Infantry.

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.)
Spells you cast during combat cost {1} less to cast.

Whenever a creature you control leaves the battlefield, if it had counters on it, you may put one of those counters on Ironpact Marauder.
{1}{B}, Remove two counters from Ironpact Marauder: You draw a card and you lose 1 life.

When Ironsmash Wrecker enters, you may destroy target artifact.

Flash
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Cadence (Whenever you cast a spell, if its mana value is greater than this creature's power, put a +1/+1 counter on this creature.)
Whenever Irreguleopard deals combat damage to a player, permutate. (You may remove a counter from a creature you control. If you do, put two +1/+1 counters on a different creature you control.)

When Irticull's Vanguard enters, exile target nonland permanent an opponent controls until Irticull's Vanguard leaves the battlefield.
Reprocess {1}{W}{W}{W} (Cast a copy of this from your graveyard by exiling it and paying {1}{W}{W}{W}. Spend only mana from differently named sources this way.)

Flying
Morph {4}{R}{W} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Ishim of Devilry is turned face up, put a +1/+1 counter on it, then each opponent loses 2 life and you gain 2 life.

Flying
Morph {3}{B}{G} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Ishim of Genesis is turned face up, put a +1/+1 counter on it, then return target instant or sorcery card from your graveyard to your hand.

Flying
Morph {3}{U}{R} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Ishim of Punishment is turned face up, put a +1/+1 counter on it, then untap another target tapped creature. Ishim of Punishment deals 3 damage to that creature.

Menace
Whenever Issbarren Creeper deals combat damage to a player, draw a card, then discard a card.

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.

Flash
When Issbarren Warden enters, exile target token.