Shelinda, Yevon Acolyte* Plenty of counters fun with Shelinda who either grows or pumps others depending on their size when they come join the party, fitting right into the Final Fantasy 10 Commander deck
"Final Fantasy Pixel Remasters reveal the secret of the series' best villains"
This would be a whole lot higher on the list except that it is also card quality, fixing and a discard outlet for your opponent as well
Hedron Crab A classic staple of Modern mill strategies, Hedron Crab turns every land drop into some milled cards
Rotation, by default, rotates several sets out of play in regular formats, meaning you can't use cards that have rotated out unless they've been reprinted
Amber glimmers sport high willpower but has rather insignificant strength stats