According to 24.0 Patch Notes (suddenly, I can’t include the link to them):
Faerie Breath 5
- Old: Deal 10 damage. Give a random friendly Merc on your bench +3/+5. → New: Deal 12 damage. Give the lowest health Merc on your bench +3/+10.
However, in the game the description still indicates a random merc.
[UPD]
After a little bit of initial testing, it appears as if the patch notes are correct on the ability’s behaviour, it is only the description that has not been properly updated.