Most Commander decks have enough targeted removal to destroy your creature once or twice, but locking the Greaves on it basically ensures theyll have to two-for-one you (perhaps Shattering the Greaves then destroying your creature) or board wipe
I am willing to put in some work
Even if you never cast the gigantic creature, the Eldrazis last ability will ensure that you never run out of cards against Mill
For four mana, it protects you and your permanents from harm for an entire turn
[24] Mechanically, this lets black get around effects that would prevent or replace damage
Vigilance is extremely strong in multiplayer, and this doesnt just give you that, but it can give you a king hit you need to maybe knock two players out in the same turn (or more , with some abilities like Myriad)