I also appreciate that Boseiju ramps your opponent
As long as neither player is manipulating their library or using their graveyard, using a Millstone does nothing but reveal information until the player being milled runs out of cards, but it took more explanation than you can possibly imagine to make players understand this
Modern cards offer similar discard-for-spell outlets, like Call the Bloodline
Plus, Clement turns all of our Frogs into mana dorks
When fighting Elmdore before he turns into a Lucavi, he shows himself as one of the few characters who uses the teleport skill in a cutscene to have it as a skill in combat, using it to teleport around the area as you fight him
Its ability scales so well with the number of opponents you have, making this 2/4 a Commander powerhouse with over 320,000 decks to its name, according to EDHREC