Its fairly easy to get a 4-power creature into play these days, or grow smaller ones, and this card supplies a steady source of card draw to green decks
Once the player fails to discard and instead mills a card, all further effects of each additional Magus of the Chains will not do anything
Duh This card came from all the abuse R&D gets over reminder text
if Zimone has four counters, you can cast multiple counterspells like Syncopate and Repulsive Mutation for relatively little mana, which makes it easy to play them alongside a draw spell like Blue Sun's Zenith for an excellent turn cycle
There were a lot of options , it was hard to decide
Because of this, I see the deck constantly switching between tier 1 and 2, depending on how the meta develops and how decks are approaching the field