Henchmen are hired Wizards that help you in a duel and they can only be purchased during your turn in combat.
They will come to your aid and behave similar to your Minion, only stronger and smarter. They will act in the same round that they are summoned by the player, and will disappear once the duel has ended.
Since Henchmen allow you to shortcut gameplay, they are only available for Crowns.