This is powerful for a number of reasons, not least because it lets you circumvent paying six, seven, eight or more mana for a haymaker, and instead enjoy its EtBs and other triggers for a smaller investment
"Mill" is a colloquial term that originates from the card Millstone, used here to mean "putting the top cards of a player's library into his or her graveyard." For example, you could say, "In the finals of the Pro Tour Qualifier, Herbert cast Tome Scour to mill away my final five cards, dashing my chances of playing on the Pro Tour." There are many players who will play with Tome Scour in their decks
Heres the starter kit for the birds-tempo deck I will keep tinkering with: #55
Until I led with it here, did you really know that there was a card called Yoke of the Damned
Then there's eerie that's a one-up on up on constellation