The Circle of Loyalty

This spell costs {1} less to cast for each Knight you control.
Creatures you control get +1/+1.
Whenever you cast a legendary spell, create a 2/2 white Knight creature token with vigilance.
{3}{W}, {T}: Create a 2/2 white Knight creature token with vigilance.

Benalish Marshal

Gallant Cavalry

Vigilance (Attacking doesn't cause this creature to tap.)
When Gallant Cavalry enters, create a 2/2 white Knight creature token with vigilance.

Militant Angel

Flying, lifelink
When Militant Angel enters, create a number of 2/2 white Knight creature tokens with vigilance equal to the number of opponents you attacked this turn.

Valiant Knight

Other Knights you control get +1/+1.
{3}{W}{W}: Knights you control gain double strike until end of turn.

Acclaimed Contender

When Acclaimed Contender enters, if you control another Knight, look at the top five cards of your library. You may reveal a Knight, Aura, Equipment, or legendary artifact card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Sigiled Sword of Valeron

Equipped creature gets +2/+0, has vigilance, and is a Knight in addition to its other types.
Whenever equipped creature attacks, create a 2/2 white Knight creature token with vigilance that's attacking.
Equip {3}

Nadaar, Selfless Paladin

Vigilance
Whenever Nadaar, Selfless Paladin enters or attacks, venture into the dungeon. (Enter the first room or advance to the next room.)
Other creatures you control get +1/+1 as long as you've completed a dungeon.

Heraldic Banner

As this artifact enters, choose a color.
Creatures you control of the chosen color get +1/+0.
{T}: Add one mana of the chosen color.

Silverwing Squadron

Flying, vigilance
Silverwing Squadron's power and toughness are each equal to the number of creatures you control.
Whenever Silverwing Squadron attacks, create a number of 2/2 white Knight creature tokens with vigilance equal to the number of opponents you have.