Thunderhead Squadron

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Flying

Protocol Knight

When Protocol Knight enters, tap target creature an opponent controls. Put a stun counter on that creature if you control another Knight. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Swordsworn Cavalier

Swordsworn Cavalier has first strike as long as another Knight entered the battlefield under your control this turn.

Ayara's Oathsworn

Menace
Whenever Ayara's Oathsworn deals combat damage to a player, if it has fewer than four +1/+1 counters on it, put a +1/+1 counter on it. Then if it has exactly four +1/+1 counters on it, search your library for a card, put it into your hand, then shuffle.

Serra Faithkeeper

Invasion of Dominaria

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When Invasion of Dominaria enters, you gain 4 life and draw a card.

Invasion of Dominaria // Serra Faithkeeper

Vertex Paladin

Flying
Vertex Paladin's power and toughness are each equal to the number of creatures you control.

Invasion of Xerex

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When Invasion of Xerex enters, return up to one target creature to its owner's hand.

Invasion of Xerex // Vertex Paladin

Xerex Strobe-Knight

Flying, vigilance
{T}: Create a 2/2 white and blue Knight creature token with vigilance. Activate only if you've cast two or more spells this turn.

Knight-Errant of Eos

Convoke
When Knight-Errant of Eos enters, look at the top six cards of your library. You may reveal up to two creature cards with mana value X or less from among them, where X is the number of creatures that convoked Knight-Errant of Eos. Put the revealed cards into your hand, then shuffle.

Zhalfirin Lancer

Whenever another Knight you control enters, Zhalfirin Lancer gets +1/+1 and gains vigilance until end of turn.

Marshal of Zhalfir

Other Knights you control get +1/+1.
{W}{U}, {T}: Tap another target creature.

Holy Frazzle-Cannon

Whenever equipped creature attacks, put a +1/+1 counter on that creature and each other creature you control that shares a creature type with it.
Equip {1}

Invasion of New Capenna

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When Invasion of New Capenna enters, you may sacrifice an artifact or creature. When you do, exile target artifact or creature an opponent controls.

Invasion of New Capenna // Holy Frazzle-Cannon

Order of the Alabaster Host

Whenever Order of the Alabaster Host becomes blocked by a creature, that creature gets -1/-1 until end of turn.

Order of the Mirror

{3}{W/P}: Transform Order of the Mirror. Activate only as a sorcery. ({W/P} can be paid with either {W} or 2 life.)

Order of the Mirror // Order of the Alabaster Host

Kithkin Billyrider

Preening Champion

Flying
When Preening Champion enters, create a 1/1 blue and red Elemental creature token.

Belenon War Anthem

Invasion of Belenon

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When Invasion of Belenon enters, create a 2/2 white and blue Knight creature token with vigilance.

Invasion of Belenon // Belenon War Anthem

Sigiled Sentinel

Backup 1 (When this creature enters, put a +1/+1 counter on target creature. If that's another creature, it gains the following ability until end of turn.)
Vigilance

Knight of the New Coalition

Vigilance
When Knight of the New Coalition enters, create a 2/2 white and blue Knight creature token with vigilance.