The decks often pack Howling Mine effects to trigger Ian and cast-from-exile payoffs like Passionate Archaeologist to exploit it further
Furthermore, its Loyalty-gaining ability let its controller cast all spells at Instant speed, creating a huge imbalance
One last thing needed to fit to produce a set that brought these two sides, fairy tales and Arthurian legend, together
Uncommon 100 Vicious Betrayal Common 101 Dr
From there, you have other cute effects such as Paradox Haze to provide you with extra upkeeps, Phyrexian Arena for more card draw, As Foretold to play cards for free, and at the end of the curve, you have decent cards like Xanathar, Guild Kingpin or Extravagant Replication that can push you ahead in games