If you control no creatures as Abzan Monument's last ability resolves, X is 0
This may not always remain the case though Magda, Brazen Outlaw is the type of card that will only get better as more cards are printed over time, and with more Dwarves seeing print these days, it is entirely possible this balance of power could shift in favor of this under supported creature tribe
Oh, and by the way, isn't it a fun five-drop after your #10
You can cast it for its harmonize cost, upping the green commitment to four but now letting you tap creatures to pay for that X cost
Incapsula incident ID: 569000121294678746-362076532047938347
So many of these could have easily made the Top 20, but considering A) that would have skewed the 20 into a list of most easy to include in all of your decks and B) would have taken multiple slots away from other cards, theyre also getting an Honorable Mention