Chorus of One is a legendary major card out of the New mechanic pool. Mending Chorus mends one ally for 20% of max health plus 20 on a 20% shorter cooldown.

You can take it once · it only turns up when your Special ability can actually use it · it can be offered for 0 of the 34 abilities.

Only one card can reshape that ability this way — this one, or Endless Chorus and Warding Chorus. Take one and the rest are gone for the run.