msem-instigator

Parish Paragon gets +1/+1 for each creature you control.
All damage that would be dealt to other creatures you control not named Parish Paragon is dealt to Parish Paragon instead.

Razing Throng's power and toughness are each equal to the number of creatures you control.
Whenever one or more cards are put into exile from anywhere, create a 1/1 white Cleric creature token.
{2}{W}{W}: Exile a nonland card from a graveyard. You gain 3 life.

Flying
Starbane Elemental's power and toughness are each equal to the number of creatures with flying you control.
When Starbane Elemental enters, destroy all creatures without flying.

Strident Retainer's power and toughness are each equal to the number of creatures you control.
Art of war — At the beginning of your end step, if Strident Retainer dealt damage to an opponent this turn, create a 1/1 colorless Samurai creature token.

Flying
Warden of Harshapal Tower's power and toughness are each equal to the number of creatures you control.

Witchseeker Mob's power and toughness are each equal to twice the number of Citizens and/or Peasants you control.
When Witchseeker Mob enters, exile target nonland permanent an opponent controls with mana value less than or equal to Witchseeker Mob's power until Witchseeker Mob leaves the battlefield.

When you cast Aspect of Shifting Storms, create a token that's a copy of it.
You may have Aspect of Shifting Storms enter as a copy of any creature on the battlefield, except if it's a token it has no mana cost.

You may have Blurry Counterpart enter as a copy of any creature on the battlefield.
Mirage {1}{U} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

You may have Ephemeral Qilin enter as a copy of a multicolored permanent you control.

You may have Fleeting Memory enter as a copy of any creature on the battlefield, except it has “At the beginning of the end step, exile this creature.”

You may have Imitator of Success enter as a copy of any creature on the battlefield, except it has no mana cost and base power and toughness 1/1 if it's a token.
Successor {1}{U}{U} ({1}{U}{U}, Exile this card from your graveyard: Create a token that's a copy of this card, except it has no mana cost and base power and toughness 1/1. Succeed only as a sorcery.)

You may have Insipid Metamorph enter as a copy of any other creature on the battlefield, except it's 1/1.

As long as you control an Island, you may cast this spell as a copy of any creature on the battlefield. (This includes casting cost.)

Flying
Nectarkin enters with a +1/+1 counter on it.
Whenever Nectarkin 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.)

You may cast this spell as though it had flash if you pay an additional {2} to cast it.
You may have Resourceful Impersonator enter as a copy of any creature on the battlefield.

You may have Shaper of the Formless enter as a copy of any creature on the battlefield, except it has “{2}{U}: Target face-down creature becomes a copy of this creature until end of turn. Turn that creature face up. At the beginning of the next cleanup step, turn it face down.”

You may have Snowfield Doppelganger enter as a copy of any creature on the battlefield, except it has “While a player is choosing targets as part of casting a spell, that player must choose at least one other creature that shares a name with this creature if able.”

Synchronous Battle Armor and equipped creature get +1/+1 for each artifact you control.
Whenever equipped creature attacks, tap up to three target creatures.
Reconfigure {3}{U}{U} ({3}{U}{U}: Attach to target creature you control; or unattach from a creature. Reconfigure only as a sorcery. While attached, this isn't a creature.)

You may have Undecided Mimic enter or phase in as a copy of any creature on the battlefield, except it has this ability and “{2}{U}{U}: Undecided Mimic phases out.” (Treat it and anything attached to it as though they don't exist until its controller's next turn.)

You may have Warped Physiognomist enter as a copy of any creature on the battlefield with mana value 3 or less.

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.)
You may have Witch of Shifting Waters enter as a copy of any creature on the battlefield, except it's an enchantment in addition to its other types.

Deathwind Survivor's power and toughness are each equal to the number of enchantments you control.
Whenever an enchantment you control enters, put a +1/+1 counter on target creature.

Menace
Evanescent Soulcatcher's power and toughness are each equal to the number of cards in exile.
{2}, Exile a card from your hand: Regenerate Evanescent Soulcatcher.

The Urchin King's power and toughness are each equal to the number of cards in all graveyards.
Sacrifice a creature: The Urchin King gains lifelink and indestructible until end of turn.

Zygos, Underworld Scourge's power and toughness are each equal to the number of cards you own in exile and in your graveyard.
Spells you cast have “As an additional cost to cast this spell, you may exile any number of cards from your graveyard. This spell costs {1} less to cast for each card exiled this way.”