The second ability represented by the "partner with [name]" keyword modifies the rules for deck construction in the Commander variant and has no function outside of that variant
Offering some cross-tribal benefits for assassins, mercenaries, and rogues, Mari seems like an excellent support card for Etrata, the Silencer due to her ability to exile enemy creatures with hit counters on them when they die
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of Urianger Augurelt's last ability)
One of my favorite precons in recent months, its Jump Scare
So although there were roughly 277K (again, this is my rough estimate) Revised Booster Boxes made, over the years that number has dwindled down as more and more got ripped open