No, the Playtest Cards from the Convention Edition Mystery Boosters are not legal in EDH
Dishonorable Mention: Lovely flavor, beautiful art, and one of the worst cards ever printed in the history of the game
Let's see how well the stock list pulls off its goals: Counter Blitz is all-in on Counters and does what it sets out to do well: I count 38 cards the put counters on either themselves or other cards, nearly all of these are +1/+1 counters but there's a bit of other stuff too (4 summon creatures put lore counters on themselves like Summon: Valefor)
Kingdra #TG3Ultra Rare $12.67 Kingdra #8Holo Rare $23.41 Kingdra #19Rare $8.69 Kingdra #12Holo Rare $5.00 Kingdra #7Holo Rare $15.86 Kingdra #17Rare $3.84 Kingdra #107Rare $0.48 Kingdra #31Holo Rare $0.63 Kingdra #33Holo Rare $0.38 Kingdra #37Holo Rare $0.30 Vanillite #27Common $0.28 Espeon (Team Plasma) #48Uncommon $5.88 Pachirisu #37Common $0.40 Beldum #50Common $0.34 Seismitoad (Team Plasma) #26Rare $0.61 Metagross (Team Plasma) #52Holo Rare $10.98 Mankey #59Common $0.34 Palpitoad #25Uncommon $0.26 Thundurus EX (Team Plasma) #38Ultra Rare $13.33 Voltorb #32Common $0.25
And If you will beg my pardon, I would like to ask you permission to make a Part 3 of this alternate art series
For each of those cards, pay 4 life or put the card on top of your library
