msem-instigator

Equipped creature gets +2/+0 and has “{T}, Unattach Javelin: It deals 2 damage to target creature.”
Equip {2}

Trample
Whenever a creature card is put into your graveyard from anywhere, put a +1/+1 counter on Jawbone, Ravenous Mutant.

As an additional cost to cast this spell, return a creature you control to its owner's hand or pay {2}.
Counter target spell.

Enspirit (As you cast this spell, you may exile a nonenchantment creature you control until this leaves the battlefield or fails to resolve. Reduce this spell's cost by the exiled card's mana value.)
{T}: The next creature spell you cast this turn has enspirit. When that creature enters, it becomes an enchantment in addition to its other types.

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

When Jeffery Stages the Finale enters, search your library for a legendary blue card, reveal it, put it into your hand, then shuffle.
Whenever you cast a spell with mana value 5 or greater, return up to one target nonland permanent to its owner's hand.

Once each turn, when Jeffery enters or you create an Aura token, you may create an Aura Role enchantment token named Lead Role attached to target creature you control. It's all colors and has enchant creature you control and “Enchanted creature has base power and toughness 5/5, is all creature types, and has flying, vigilance, trample, lifelink, and prowess.”
Whenever an enchanted creature you control attacks, draw a card.

Bloodprice {B}{B}{B}{B} (You may cast this card by sacrificing a creature and paying its bloodprice.)
Lifelink, haste
Sacrifice another Demon: Jejun, Dark Hunter gains flying and indestructible until end of turn.

Enchant creature
Enchanted creature gets +3/+3, has flying, and “{1}{W}: Put a +1/+1 counter on this creature.”

Flying
Once during each of your turns, for each creature you control, you may activate one of that creature's activated abilities with {T} in its cost without paying {T} and as though that creature had haste.

Motley — This spell costs {3} less to cast as long as there are five or more names among nonland permanents you control.
Destroy all creatures.

Whenever a creature you control enters, put a loyalty counter on Jenn, the Rising Dawn.
[0]: Target creature you control gets +1/+1 and gains first strike and lifelink until end of turn.
[–5]: Exile target creature.

Audition for green, then audition for green. (Create a 1/1 Construct Actor creature token, a Scout Role giving 2/3 and vigilance, or a Warrior Role giving 3/2 and trample. Roles replace older ones.)

When Jerrold's Wretched Cure enters, search your library for a legendary green card, reveal it, put it into your hand, then shuffle.
At the beginning of your upkeep, up to one other target nonland permanent you control becomes an X/X Construct creature in addition to its other types until end of turn, where X is the number of card types among cards in your graveyard.

Lifelink
Whenever Jerrold, Fugitive or another creature you control enters, if you cast it, you may cast target instant or sorcery card from your graveyard with lesser mana value by paying life equal to its mana value rather than paying its mana cost. Exile that card instead of putting it anywhere else as it resolves.

Creatures you control have “Whenever this creature attacks, put a +1/+1 counter on target creature with lesser power.”
At the beginning of each end step, if there are five or more +1/+1 counters among creatures you control, destroy up to one target artifact or enchantment.

Choose two —
• Attacking creatures target player controls get +2/+0 and gain first strike until end of turn.
• Jeska's Command deals 3 damage to target creature.
• Creatures target player controls without flying can't block this turn.
• Target player exiles the top card of their library. Until the end of their next turn, they may play that card.

[+2]: Up to one target creature gets +1/+0 and gains first strike and haste until end of turn.
[–3]: Jeska deals 3 damage to target creature. If that creature is an artifact, she deals 5 damage instead.
[–10]: You get an emblem with “Creatures you control get +2/+0.” and “All creatures have haste and can't block.”

Hexproof
At the beginning of each end step, if an opponent was dealt 4 or more damage this turn, return target instant or sorcery card from your graveyard to your hand.

Advance {2} (Cast this for {2} to advance it as it enters. {2}: Advance this as a sorcery.)
Equipped creature gets +X/+0 and has flying, where X is the number of times it and Jet Pack have advanced this turn.
Equip {1}

Each player sacrifices a creature and discards a card.
Fuse (You may cast one or both halves of this card from your hand.)

Haste
When Jetskate enters, if you've drawn two or more cards this turn, it deals 2 damage to any target.
Cycling {R} ({R}, Discard this card: Draw a card.)

Flash
{1}{W}: Jhessian Cavalier gains lifelink until end of turn.

Reach
Whenever another creature you control becomes the target of an instant or sorcery spell, that creature gets +3/+3 until end of turn.

When Jidai Clairvoyant enters, create a 2/2 colorless Spirit creature token.
Whenever a colorless creature you control enters, you may draw a card.