msem-instigator

Whenever you cast a noncreature spell, upgrade Indecisive Sorceress. When you can't, remove all counters from it and it deals damage to any target equal to the number of counters removed this way.
• +1/+1
• Flying
• First strike

When Indomitable Duo enters the battlefield, choose up to two creature card names.
Whenever Indomitable Duo attacks, put a +1/+1 counter on each creature you control with a name chosen by Indomitable Duo.

{W}{B}, Shuffle Inexorable Explorer into your library: Return target creature card from your graveyard to the battlefield.
{W}{B}, Sacrifice a creature: Return Inexorable Explorer from your graveyard to the battlefield tapped.

When Infamous Bilgecaptain enters the battlefield, forebode. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.)
Other Pirates you control get +1/+1.
At the beginning of your end step, you may put a Pirate card with mana value less than or equal to the number of artifacts you control from your hand onto the battlefield.

When Infectious Corpse dies, each player loses 2 life.

Haste
When Inferno Forerunner enters the battlefield, you may have target creature gain haste until end of turn.

Flying, prowess
Whenever you cast a noncreature spell, untap Ingenious Trickster.

Whenever you cast a spell, untap Inglorious Blaze.
{T}: Inglorious Blaze deals 1 damage to target player or planeswalker.

When Ink Seer dies, you draw a card, lose 1 life, and create a Treasure token.

Whenever Inkwell Daggers enters the battlefield or attacks, proliferate. (Choose any number of permanents and/or players with counters on them, then give each another counter of each kind already there.)

When Inner-Eye Obscurist enters the battlefield, return each other creature that isn't in Inner-Eye Obscurist's pack to their owners' hand. (Two or more creatures you control with equal power are in a pack.)

{T}: Add {U} or {R}. Spend this mana only to cast an instant, sorcery, or Wizard spell.
Whenever you cast your second spell each turn, untap Innova.

Whenever a creature enters the battlefield under your control for the second time each turn, it gains haste until end of turn. You may have it get +1/+1 until end of turn.

Vigilance
When Inquisitive Student enters the battlefield, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Whenever Insatiable Abomination or another Horror enters the battlefield under your control, each player mills four cards.
Exile a creature card from your graveyard: Tap target Horror you control. It gains indestructible until end of turn.

Whenever a creature you control dies, Insidious Terror gets +1/+0 and gains menace until end of turn.

When Inspired Blade enters the battlefield, if you control another Warrior, draw a card.

Trial 3 (As you cast this spell, an opponent of your choice may pay 3 life. If they don't, they fail the trial.)
When Inspired Trialmaker enters the battlefield, if the trial was failed, add {R}{W}{B}.

Harmony — Target creature gets +2/+2 until end of turn.
When Inspiring Band enters the battlefield, harmonize. (Trigger up to one harmony of one permanent you control.)

When Insurgent Racketeer enters the battlefield or dies, you may discard a card. If you do, draw a card.

When Intrepid Shieldmate enters the battlefield, target creature gets +1/+1 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.

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, trample, lifelink