Most cards on this list let you double +1/+1 counters, like Kalonian Hydra, since theyre the most common kind, while others let you double any type of counter
$1.99 Gandalf of the Secret Fire (0507 - Borderless) The Lord of the Rings: Tales of Middle-earth Commander Decks Variants $0.49 Timecrafting Planar Chaos $6.99 Twenty-Toed Toad Bloomburrow Commander Decks $0.39 Shadow Alley Denizen Gatecrash $0.35 Jhoira's Timebug Time Spiral $1.29 Infinite Hourglass Ice Age $4.99 Approach of the Second Sun Amonkhet $2.79 Mystic Sanctuary Throne of Eldraine $0.39 Clockspinning Time Spiral $5.99 Voltaic Key 2011 Core Set $0.59 Dust of Moments Future Sight $0.39 Drainpipe Vermin Return to Ravnica 0 results found
You also have the choice of dueling generic opponents on the map or participating in tournaments
Mysterious Treasures Images, Press Release - Mysterious Treasures , the second Diamond and Pearl set (called Mystery of the Lakes in Japan), now has an American press release, which you can read below
Commander cheat-sheet
Eyes of the Abyss Fusion Summon 1 "Eyes Restrict" Fusion Monster from your Extra Deck, using monsters from your hand or either side of the field as Fusion Materials, then if 1 monster from each side of the field was used as Fusion Materials, you can send 1 monster that specifically lists the card "Relinquished" in its text from your Deck to the GY
