I played a match a while ago and in that match I played a Golden Monkey after previously having played a Mistcaller. My hand got replaced, and as expected, those cards all lost the Mistcaller buff.
But, to my surprise, the legendaries I drew from my deck retained the Mistcaller +1/+1 buff.
Is Mist Caller placing a buffed state that triggers when ever I draw a card, rather than buffing cards of my deck in place?
Best Answer
Mist caller creates an On-draw trigger to apply the +1/+1 buff to any minion cards drawn from the deck to your hand. Cards pulled from the deck via other means (for example, by Deathlord) bypass this trigger and thus do not get the buff. In addition, cards added to your deck after playing mistcaller (for example, via Entomb) will get the buff.
You can look at the Advanded Rule Book, specifically the Drawing a card section for a lot of details about how card draws and effects tied to it work.
For now, the way this works is not considered a bug. Ben Brode tweeted at one point it is was implemented this way do to server performance concerns