Have

Leyline of Singularity

If Leyline of Singularity is in your opening hand, you may begin the game with it on the battlefield.
All nonland permanents are legendary.

Proxied

Dreamroot Cascade

Dreamroot Cascade enters tapped unless you control two or more other lands.
{T}: Add {G} or {U}.

Doric, Owlbear Avenger

Vigilance, trample
When this creature transforms into Doric, Owlbear Avenger, other legendary creatures you control get +2/+2 and gain trample until end of turn.
At the beginning of your upkeep, transform Doric.

Doric, Nature's Warden

Vigilance
When Doric, Nature's Warden enters, search your library for a Forest card, put it onto the battlefield tapped, then shuffle.
Whenever Doric attacks, you may pay {1}{G}. If you do, transform her.

Doric, Nature's Warden // Doric, Owlbear Avenger

Rivendell

Rivendell enters tapped unless you control a legendary creature.
{T}: Add {U}.
{1}{U}, {T}: Scry 2. Activate only if you control a legendary creature.

Worldspine Wurm

Trample
When Worldspine Wurm dies, create three 5/5 green Wurm creature tokens with trample.
When Worldspine Wurm is put into a graveyard from anywhere, shuffle it into its owner's library.

Rona, Tolarian Obliterator

Trample
Whenever a source deals damage to Rona, Tolarian Obliterator, that source's controller exiles a card from their hand at random. If it's a land card, you may put it onto the battlefield under your control. Otherwise, you may cast it without paying its mana cost.

Rona, Herald of Invasion

Whenever you cast a legendary spell, untap Rona, Herald of Invasion.
{T}: Draw a card, then discard a card.
{5}{B/P}: Transform Rona. Activate only as a sorcery. ({B/P} can be paid with either {B} or 2 life.)

Rona, Herald of Invasion // Rona, Tolarian Obliterator

Island

Forest

Jalira, Master Polymorphist

{2}{U}, {T}, Sacrifice another creature: Reveal cards from the top of your library until you reveal a nonlegendary creature card. Put that card onto the battlefield and the rest on the bottom of your library in a random order.

Reki, the History of Kamigawa

Whenever you cast a legendary spell, draw a card.

Great Hall of the Citadel

{T}: Add {C}.
{1}, {T}: Add two mana in any combination of colors. Spend this mana only to cast legendary spells.

The Ringhart Crest

As The Ringhart Crest enters, choose a creature type.
{T}: Add {G}. Spend this mana only to cast a creature spell of the chosen type or a legendary creature spell.

Kolvori, God of Kinship

As long as you control three or more legendary creatures, Kolvori gets +4/+2 and has vigilance.
{1}{G}, {T}: Look at the top six cards of your library. You may reveal a legendary creature card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Kolvori, God of Kinship // The Ringhart Crest

Karn's Temporal Sundering

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Target player takes an extra turn after this one. Return up to one target nonland permanent to its owner's hand. Exile Karn's Temporal Sundering.

Champion's Helm

Equipped creature gets +2/+2.
As long as equipped creature is legendary, it has hexproof. (It can't be the target of spells or abilities your opponents control.)
Equip {1}

Mobilized District

{T}: Add {C}.
{4}: Mobilized District becomes a 3/3 Citizen creature with vigilance until end of turn. It's still a land. This ability costs {1} less to activate for each legendary creature and planeswalker you control.

Shoot Down

Exile target artifact, enchantment, or creature with flying.

K-9, Mark I

Negative — As long as K-9, Mark I is untapped, other legendary creatures you control have ward {1}.
Affirmative — {1}{U}, {T}: Target legendary creature can't be blocked this turn.
Doctor's companion (You can have two commanders if the other is the Doctor.)

Arasta of the Endless Web

Reach
Whenever an opponent casts an instant or sorcery spell, create a 1/2 green Spider creature token with reach.

Kamahl's Druidic Vow

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Look at the top X cards of your library. You may put any number of land and/or legendary permanent cards with mana value X or less from among them onto the battlefield. Put the rest into your graveyard.

Mirror Box

The "legend rule" doesn't apply to permanents you control.
Each legendary creature you control gets +1/+1.
Each nontoken creature you control gets +1/+1 for each other creature you control with the same name as that creature.