"As peace should be—gentle yet unstoppable."
—Augustin IV

The List

Azorius Herald

Azorius Herald can't be blocked.
When Azorius Herald enters, you gain 4 life.
When Azorius Herald enters, sacrifice it unless {U} was spent to cast it.

RNA Guild Kit

Azorius Herald can't be blocked.
When Azorius Herald enters the battlefield, you gain 4 life.
When Azorius Herald enters the battlefield, sacrifice it unless {U} was spent to cast it.

Commander 2013

Dissension

Azorius Herald is unblockable.
When Azorius Herald comes into play, you gain 4 life.
When Azorius Herald comes into play, sacrifice it unless {U} was spent to play it.