It does most of what a Fiend/Maggot does with their EtB effects and then it is better at staying in play, far better at blocking, enables raid, controls planeswalkers and is generally a pain in the arse
Riverchurn Monument is the kind of mill card that scares me, because it tends to combo with a bunch of mill favorites like Bruvac, Phenax, God of Deception, and ways to make players mill a lot of cards (Maddening Cacophony, anyone?)
You could initially get this card signed at character meet and greets that occurred during the cards distribution
And the entire hero team also has 60 life
Here is what each booster type will contain according to the official WOTC release: Play Booster: 14 cards 5 Single-faced common cards 1 Double-faced common card 3 Uncommon cards There is a 0.6% chance for an equinox treatment uncommon here or in the wildcard slot