Aight! ın the quests section of the game there are alot of quests every day and you can re-request one of them once per day so if you happen to have a quest which you don't fancy doing it, then there is a possibility that you might be able to finish it and without even playing or spending time on it!
So the quests does not care whether if you play ranked or casual all you need to do is to create a deck with the shown characters by going here:
And when you do you just add a random deck with random cards of a given character i.e shaman
And just continue filling your deck with arbitrary cards
Because you don't have to win the game, all they ask you to play the game (but there is no way to confirm whether if you really play or if you just press the play button and stay afk, cook some food etc xD
So you can change your game mode from ranked to casual
Or you can even play in one of other ranked mode which you don't pursue a league level
If you are like me and if you know that you can't go below a certain level because you have somehow hit the checkpoint, you can even stay at your own league
In my case i know from experience that i can't go below wild 10 even if i lose 1000 times, i can just press play button and let the opponent kill me by staying afk or cooking some food and i still get rewarded and it is a bug in the game, a bug that most people that are not aware of (including Blizzard Studios, one of the biggest in the world right now)