Gandalf the White

Flash
You may cast legendary spells and artifact spells as though they had flash.
If a legendary permanent or an artifact entering or leaving the battlefield causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

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.

Merry, Warden of Isengard

Partner with Pippin, Warden of Isengard (When this creature enters the battlefield, target player may put Pippin into their hand from their library, then shuffle.)
Whenever one or more artifacts enter the battlefield under your control, create a 1/1 white Soldier creature token with lifelink. This ability triggers only once each turn.

Frodo Baggins

Whenever Frodo Baggins or another legendary creature enters the battlefield under your control, the Ring tempts you.
As long as Frodo is your Ring-bearer, it must be blocked if able.

Aragorn, the Uniter

Whenever you cast a white spell, create a 1/1 white Human Soldier creature token.
Whenever you cast a blue spell, scry 2.
Whenever you cast a red spell, Aragorn, the Uniter deals 3 damage to target opponent.
Whenever you cast a green spell, target creature gets +4/+4 until end of turn.

Pippin, Guard of the Citadel

Vigilance, ward {1}
{T}: Another target creature you control gains protection from the card type of your choice until end of turn. (It can't be blocked, targeted, dealt damage, enchanted, or equipped by anything of that type.)

Boromir, Warden of the Tower

Vigilance
Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell.
Sacrifice Boromir, Warden of the Tower: Creatures you control gain indestructible until end of turn. The Ring tempts you.

Samwise Gamgee

Whenever another nontoken creature enters the battlefield under your control, create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this artifact: You gain 3 life.")
Sacrifice three Foods: Return target historic card from your graveyard to your hand. (Artifacts, legendaries, and Sagas are historic.)

Samwise the Stouthearted

Flash
When Samwise the Stouthearted enters the battlefield, choose up to one target permanent card in your graveyard that was put there from the battlefield this turn. Return it to your hand. Then the Ring tempts you.

Gimli of the Glittering Caves

Double strike
Whenever another legendary creature enters the battlefield under your control, put a +1/+1 counter on Gimli of the Glittering Caves.
Whenever Gimli deals combat damage to a player, create a Treasure token.

Legolas Greenleaf

Reach
Legolas Greenleaf can't be blocked by creatures with power 2 or less.
Whenever another legendary creature enters the battlefield under your control, put a +1/+1 counter on Legolas Greenleaf.
Whenever Legolas Greenleaf deals combat damage to a player, draw a card.

Pippin, Warden of Isengard

Partner with Merry, Warden of Isengard (When this creature enters the battlefield, target player may put Merry into their hand from their library, then shuffle.)
{1}, {T}: Create a Food token.
{T}, Sacrifice four Foods: Other creatures you control get +3/+3 and gain haste until end of turn. Activate only as a sorcery.