Urza's Ruinous Blast

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Exile all nonland permanents that aren't legendary.

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.

Captain Sisay

{T}: Search your library for a legendary card, reveal that card, put it into your hand, then shuffle.

Reki, the History of Kamigawa

Whenever you cast a legendary spell, draw a card.

Flowering of the White Tree

Legendary creatures you control get +2/+1 and have ward {1}.
Nonlegendary creatures you control get +1/+1.

Elesh Norn, Grand Cenobite

Vigilance
Other creatures you control get +2/+2.
Creatures your opponents control get -2/-2.