At the moment, its hard to say
Reshiram ex - 166/086 Reshiram ex is the kind of card that becomes scarier the longer the game goes on
Of course, this is made easier by the fact that each deck contains a Sol Ring (#1 card in Commander) and a Commander's Sphere (#3 card in Commander), but Open Hostility gets both Skullclamp and Lightning Greaves, which rank in the top 20 cards in Commander
Mana-Charged Dragon isnt a hyper-powerful card, but it actually captures the concept of teaming up with individual players instead of just helping the entire table equally
April O'Neil, Kunoichi Trainee Azra Smokeshaper Biting-Palm Ninja Blade-Blizzard Kitsune Casey & Raph, Hotheads Chrome Dome Coiling Stalker Covert Technician Dark Leo & Shredder Definitely Not a Turtle Dokuchi Shadow-Walker Dokuchi Silencer Don & Leo, Problem Solvers Don & Raph, Hard Science Donatello, Gadget Master Donatello, Mutant Mechanic Donatello, Rad Scientist Donatello, Turtle Techie Donatello, Way with Machines Donatello, the Brains Donnie & April, Adorkable Duo Elektra, Daughter of the Hand Fallen Shinobi Fang of Shigeki Foot Elite Foot Mystic Foot Ninjas Futurist Operative Heroes in a Half Shell Higure, the Still Wind Ingenious Infiltrator Ink-Eyes, Servant of Oni Inkrise Infiltrator Jennika, Bad Apple Big Sister Kappa Tech-Wrecker Karai, Future of the Foot Kotose, the Silent Spider Koya, Death from Above Krang & Shredder Leonardo, Big Brother Leonardo, Cutting Edge Leonardo, Leader in Blue Leonardo, Sewer Samurai Leonardo, Worldly Warrior Leonardo, the Balance Lita, Little Orphan Amphibian Masterful Ninja Mechanized Ninja Cavalry Michelangelo, Game Master Michelangelo, Improviser Michelangelo, Mutant BFF Michelangelo, On the Scene Michelangelo, Weirdness to 11 Michelangelo, the Heart Mikey & Don, Party Planners Mikey & Leo, Chaos & Order Mikey & Mona, Mutant Sitters Mist-Syndicate Naga Mistblade Shinobi Moon-Circuit Hacker Moonblade Shinobi Moonsnare Specialist Mukotai Ambusher Nashi, Moon Sage's Scion Nashi, Searcher in the Dark Nezumi Prowler Ninja Ninja of the Deep Hours Ninja of the Hand Ninja of the New Moon Okiba-Gang Shinobi Orochi Soul-Reaver
At any rate, these key cards will likely keep rising in price between now and then
