Frontier Warmonger

Whenever one or more creatures attack one of your opponents or a planeswalker they control, those creatures gain menace until end of turn.

Izzet Signet

Bastion Protector

Commander creatures you control get +2/+2 and have indestructible.

Théoden, King of Rohan

Whenever Théoden, King of Rohan or another Human enters the battlefield under your control, target creature gains double strike until end of turn.

Prince Imrahil the Fair

Whenever you draw your second card each turn, create a 1/1 white Human Soldier creature token.

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Unbreakable Formation

Creatures you control gain indestructible until end of turn.
Addendum — If you cast this spell during your main phase, put a +1/+1 counter on each of those creatures and they gain vigilance until end of turn.

Aragorn, King of Gondor

Vigilance, lifelink
When Aragorn, King of Gondor enters the battlefield, you become the monarch.
Whenever Aragorn attacks, up to one target creature can't block this turn. If you're the monarch, creatures can't block this turn.

Sol Ring

Champions of Minas Tirith

When Champions of Minas Tirith enters the battlefield, you become the monarch.
At the beginning of combat on each opponent's turn, if you're the monarch, that opponent may pay {X}, where X is the number of cards in their hand. If they don't, they can't attack you this combat.

Selfless Squire

Flash
When Selfless Squire enters the battlefield, prevent all damage that would be dealt to you this turn.
Whenever damage that would be dealt to you is prevented, put that many +1/+1 counters on Selfless Squire.

Faramir, Steward of Gondor

Whenever a legendary creature with mana value 4 or greater enters the battlefield under your control, you become the monarch.
At the beginning of your end step, if you're the monarch, create two 1/1 white Human Soldier creature tokens.

Arcane Signet

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

Boromir, Gondor's Hope

Whenever Boromir, Gondor's Hope enters the battlefield or attacks, look at the top six cards of your library. You may reveal a Human or artifact card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Azorius Signet

Éomer, King of Rohan

Double strike
Éomer, King of Rohan enters the battlefield with a +1/+1 counter on it for each other Human you control.
When Éomer enters the battlefield, target player becomes the monarch. Éomer deals damage equal to its power to any target.

Crown of Gondor

Equipped creature gets +1/+1 for each creature you control.
When a legendary creature enters the battlefield under your control, if there is no monarch, you become the monarch.
Equip {4}. This ability costs {3} less to activate if you're the monarch.

Archivist of Gondor

When your commander deals combat damage to a player, if there is no monarch, you become the monarch.
At the beginning of the monarch's end step, that player draws a card.

Denethor, Stone Seer

When Denethor, Stone Seer enters the battlefield, scry 2.
{3}{R}, {T}, Sacrifice Denethor: Target player becomes the monarch. Denethor deals 3 damage to any target.