Dominaria United: Plaza of Heroes
: Add .
: Add one mana of any color. Spend this mana only to cast a legendary spell.
: Add one mana of any color among legendary permanents you control.
, , Exile Plaza of Heroes: Target legendary creature gains hexproof and indestructible until end of turn.
This is an instant staple of Commander decks far and wide, and don't sleep on its potential in other Constructed formats too. Protecting a legendary creature can be quite useful in many formats.