I don't think it really fits a miracle type deck. For it to work with auctioneer, you need a 6 mana 4/4 to actually survive a round. If it does, you're not going to want to copy it, you're going to want to draw more cards or win the game. For it to work with malygos, you need malygos to survive a round. If that happens, you probably have already won the game, but if you haven't, I don't think copying malygos is going to do it. If you have the spells, you win, if you don't and you copy malygos, then you have a 1/1 without spells to use.
Shadowstep worked with auctioneer because it's a 0 mana spell. This is a 5 mana minion. I don't think you run this over azure drake because miracle doesn't run enough minions in the first place to really benefit.
Maybe there is a different version of miracle and I'm just not seeing it.
Other minions that miracle runs are like tomb pillager due to getting coin. Do you really wanna spend 5 mana to then spend 1 mana to gain a coin? Seems weak and requires pillager to actually survive a round. Does it combo well with violet teacher? No, because getting a 1/1 that spawns other 1/1s just dies to any aoe. It's just too all in to lose to an AOE. Do you combo it with xaril? Perhaps that is the only minion, and seeing as it is a 3/2 for 4, chances are it will not be surviving the round to be copied. But it might be worth having available in say a more minion oriented deck.
Shadowcaster supports a more minion oriented game plan. Azure drake supports a more spell oriented game plan, plus it cycles towards more combo pieces.
I wonder what the absolute best minion in the game to copy is. I guess it might be n'zoth.