Dovin's Veto

This spell can't be countered.
Counter target noncreature spell.

Knight of the New Coalition

Vigilance
When this creature enters, create a 2/2 white and blue Knight creature token with vigilance.

Paladin Class

(Gain the next level as a sorcery to add its ability.)
Spells your opponents cast during your turn cost {1} more to cast.
{2}{W}: Level 2
Creatures you control get +1/+1.
{4}{W}: Level 3
Whenever you attack, until end of turn, target attacking creature gets +1/+1 for each other attacking creature and gains double strike.

Absorb

Templar Knight

Vigilance
{W}, Tap five untapped attacking creatures you control named Templar Knight: Search your library for a legendary artifact card, put it onto the battlefield, then shuffle.
A deck can have any number of cards named Templar Knight.

Marshal's Anthem

Multikicker {1}{W} (You may pay an additional {1}{W} any number of times as you cast this spell.)
Creatures you control get +1/+1.
When this enchantment enters, return up to X target creature cards from your graveyard to the battlefield, where X is the number of times this enchantment was kicked.

Paladin's Arms

Job select (When this Equipment enters, create a 1/1 colorless Hero creature token, then attach this to it.)
Equipped creature gets +2/+1, has ward {1}, and is a Knight in addition to its other types.
Lightbringer and Hero's Shield — Equip {4} ({4}: Attach to target creature you control. Equip only as a sorcery.)

Kwende, Pride of Femeref

Double strike
Creatures you control with first strike have double strike.

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.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Paladin of Atonement

At the beginning of each upkeep, if you lost life last turn, put a +1/+1 counter on this creature.
When this creature dies, you gain life equal to its toughness.

Haytham Kenway

Protection from Assassins
Other Knights you control get +2/+2 and have protection from Assassins.
When Haytham Kenway enters, for each opponent, exile up to one target creature that player controls until Haytham Kenway leaves the battlefield.

Last Thoughts

Draw a card.
Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

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 this Siege enters, return up to one target creature to its owner's hand.

Invasion of Xerex // Vertex Paladin

Kithkin Billyrider

Knights of Dol Amroth

Whenever you draw your second card each turn, put a +1/+1 counter on this creature.

Marshal of Zhalfir

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

Herald's Horn

As this artifact enters, choose a creature type.
Creature spells you cast of the chosen type cost {1} less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.

Order of the Alabaster Host

Whenever this creature becomes blocked by a creature, the blocking creature gets -1/-1 until end of turn.

Order of the Mirror

{3}{W/P}: Transform this creature. 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

Think Twice

Draw a card.
Flashback {2}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Zhalfirin Lancer

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

Inspiring Paladin

During your turn, this creature has first strike. (It deals combat damage before creatures without first strike.)
During your turn, creatures you control with +1/+1 counters on them have first strike.