Shyren's Agent was added in Beta 39.1.
When played, it can restore 4 HP to a damaged monster (the same amount healed by Shyren). For each excess HP healed, Agent receives a +1/+1 bonus.
This means that if it healed a monster that only needed to restore 1 HP to end up at full health, Agent gains +3/+3, for a maximum total of 7/7.