msem-instigator

If another creature with a +1/+1 counter on it you control would die, instead remove a counter from it. If you do, it phases out. (Treat it and anything attached to it as though they don't exist until its controller's next turn.)

Kernel Barrage deals damage to target creature or planeswalker equal to the number of spells you've cast this turn (including this one).
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Choose one or both —
• Destroy target enchantment.
• Return target artifact card from your graveyard to your hand.

{3}{W}: Tap target creature with power 4 or greater.

Choose one —
• Cast Judgment deals 3 damage to target attacking creature.
• Exile target artifact or enchantment.

({T}: Add {U}.)
Cloudbank enters tapped.
When Cloudbank enters, target creature gains flying until end of turn.

You may tap two untapped red creatures and/or planeswalkers you control with different names rather than pay this spell's mana cost.
Exile the top two cards of your library. Until the end of your next turn, you may play those cards.

Scry 3, then reveal the top card of your library. Discard your hand, then draw cards equal to that card's mana value.

Saljan, Lord of the Disfigured and other Mutants you control get +1/+1 and have indestructible.
Whenever Saljan attacks or blocks, create a 1/2 black Mutant creature token.

Whenever a creature you control deals combat damage to a player this turn, add that much {R}. Until end of turn, you don't lose this mana as steps and phases end.

As an additional cost to cast this spell, sacrifice a land.
Search your library for up to two basic land cards, put them onto the battlefield, then shuffle.

Advance {1}{B} (Cast this for {1}{B} to advance it as it enters. {1}{B}: Advance this as a sorcery.)
Whenever Scarcrawler advances, you lose life equal to its power, then put a +1/+1 counter on it.

Whenever Power of Redemption attacks, choose one —
• Remove all -1/-1 counters from all creatures you control.
• Untap all creatures you control.

When Arcor-Staff Adherent enters, you may remove all -1/-1 counters from target creature.

Flash
When Reinforced Platemail enters, you may attach it to target creature you control.
Equipped creature you control gets +1/+2.
Equip {3}

Spinerock Canyon enters tapped unless you control a basic land.
{T}: Add {R} or {W}.

Choose one —
• Create two 1/1 black Worm creature tokens.
• Put up to two target cards from your graveyard on top or bottom of your library.

Opera House enters tapped.
When Opera House enters, add one mana of any color.
{T}, Sacrifice Opera House: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Search your library for an instant or sorcery card, reveal it, put it into your hand, then shuffle.

When Atrocity of Flesh enters, destroy target nonland permanent.
When Atrocity of Flesh dies, you may exile it. If you do, return target card from your graveyard to your hand.

{T}: Add {C}.
{2}, {T}: Add three mana of any one color.

Equipped creature gets +1/+0, has no name, and loses all non-Pirate, non-Rogue creature types.
{1}: Equipped creature gains the creature types and activated abilities of target creature and its name becomes that creature's name until end of turn.
Equip {1}

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Destroy target creature you don't control with the greatest power.
II — Until your next turn, prevent all damage that would be dealt to you and planeswalkers you control.
III — Exile target card from a graveyard. You gain 2 life.

Enchant creature
When Crowning Ceremony enters, draw a card.
Enchanted creature gets +1/+0.

Whenever another creature or enchantment you control enters, you gain 1 life.
{3}{W}{W}, Pay 5 life: Castigated Sister becomes a 5/5 Angel Horror with flying. (This effect doesn't end at end of turn.)