msem-instigator

As an additional cost to cast this spell, discard a card.
Create three 1/1 red Soldier creature tokens with haste.

As long as it's not your turn, Northrime Amalgam gets -2/+2.

Trample, haste
When Tyrants of Bundan enters, tap all lands target player controls. They don't untap during their controller's next untap step.

This spell costs {1} less to cast for each card you've discarded this turn.
Draw three cards.

When Gusma's Artisan enters, search your library for a card, then shuffle and put that card on the bottom of it.
{2}{U}, Sacrifice Gusma's Artisan: Manifest the bottom card of your library. (To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)

Flash
Menagerie — When Seven Seas Scourge enters, if there are five or more creature types among creatures you control, counter target spell with mana value 4 or less.

Return target creature to its owner's hand. Another target creature gets -6/-0 until end of turn.

Lifelink
Whenever another creature you control enters, Hungering Cult deals 3 damage to it.

Vanishing 3 (This permanent enters with three time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
Whenever a time counter is removed from Thespian's Finale, create a token that's a copy of target creature. Sacrifice that token at the beginning of your next upkeep.

Enchant creature
{X}{B}: Enchanted creature gets +X/+X until end of turn.
When enchanted creature dies, return it to the battlefield under your control.

Target creature gets +3/-3 until end of turn.
Kindle 3—{B}{R}, Pay 3 life. ({B}{R}, Pay 3 life, Exile this card from your graveyard: Create three 1/1 colorless Elemental creature tokens. Kindle only as a sorcery.)

When Boundary Hallowblade enters, create a white Aura enchantment token named Consecration Blessing attached to target land. The token has enchant land and “Enchanted land is named Hallowed Ground and has indestructible.”

Assault {X}{R}{R} (Whenever this attacks, if it has no +1/+1 counters on it, you may pay its assault cost to put a +1/+1 counter on it.)
Other Elementals you control get +1/+0.
When Unbound Annihilus assaults, create X 1/1 red Elemental creature tokens that are tapped and attacking.

{2}, {T}: Tap target creature. This ability costs {2} less to activate if you control an enchantment.

When Distilled Inspiration enters, draw a card, then choose a card name.
{1}, {T}: Add one mana of any color.
{T}: Add one mana of any color. Spend this mana only to cast a spell with the chosen name or activate an ability of a card with the chosen name.

({T}: Add {R} or {G}.)
Practice Range enters tapped unless you control two or more basic lands.

Exile target creature. That creature's controller reveals cards from the top of their library until they reveal a creature card. That player puts that card onto the battlefield, then shuffles the rest into their library.

Voracious 1 (As this enters, you may sacrifice an artifact or creature. If you do, it enters with a +1/+1 counter on it.)
At the beginning of combat on your turn, if you sacrificed a permanent this turn, target creature you control gains trample and haste until end of turn.

Enchant creature (Target a creature as you cast this. This card enters attached to that creature.)
Enchanted creature gets +2/+1 and has trample.

Prowess
Disgraced 2 (This enters with two -1/-1 counters. Whenever it deals combat damage to a player, remove all -1/-1 counters from it.)

Vigilance
When Paired Pathfinders enters, if three or more colors were spent to cast it, create a 1/1 colorless Servo artifact creature token.

Angelfire deals X damage to up to one target.
If only {R} was spent to cast this spell and X is 5 or more, Angelfire deals X damage to each opponent and each creature and planeswalker your opponents control instead.

Destroy target creature with power or toughness 2 or less.

Haste
Ward—Sacrifice a creature.
Spinning Gears Abomination enters with X +1/+1 counters on it.
Spinning Gears Abomination can't attack alone.

When Charming Marauder enters, you may destroy target artifact or enchantment.
Recite {2}{W} (You may cast this creature from your graveyard for its recite cost. If you do, exile it when it enters or if it would leave the battlefield.)