mill cards mtg standard Blue/Black Commander Deck - Custom Built - Elite - - EDH Developing] Mono-Blue Mill (Pre-GC) -

For other specifics pertaining to how Equipment work, you should refer to the Comprehensive Rules, starting at section 301.5

In casual play, its simply a card you own thats not in your starting deck

If the card has any mandatory additional costs (such as that of Lesser Masticore), you must pay those to cast the card.

They use their mastery of time and space to wipe out any potential of the Eldrazi ever returning

Saving your commander at a critical point and not having to deal with paying two extra mana to recast him each time hes been put back in the command zone becomes better and better as the game progresses, so be sure to make use of it

Ultimately, it's a strategy to keep the game engaging for long-term collectors and to add more layers to the thrill of the hunt