If you have no other action going on and a bunch of cantrips, you can wait until you have an open mana to cycle a cantrip and get a Monk token
Avacyn breaks games in seconds
Itll also be the home for any unbanned but still powerful cards, as we saw with unbans like Gifts Ungiven and Coalition Victory being demoted from banned to Game Changers
On top of that, it reads: At the beginning of your next main phase, add an amount of colourless mana equal to that spells mana value." Basically, not only do you get to say no to something, you also get to cast something bigger on your next turn
Both scale very well with shuffle and scry effects and offer greatly more card quality as a result
Even though it costs six mana to activate, the surprise factor alone is worth it