Note: because his ability includes the word "then", you must successfully ready Mendor in order for each player to draw 1 card. So if he's not exhausted when you defeat a quest card, you don't get to draw cards. See the Rules Reference p.17 under "Then".
Wow though, he seems tailor-made to make the Angmar Awakened campaign more new-player friendly. All those side quests! I'm glad you can officially bring him into it.