Playtest cards aren’t legal for play in any tournament format other than Mystery Booster Limited formats. On the other hand, we expect they will spice up a wide variety of non-tournament games (as long as everyone’s on the same page about using them!).
You can cast Essence of Ajani as a spell. If the spell is countered, it is put into its owner’s graveyard. But if the spell resolves, its owner puts it into the command zone.
Playtest cards use a modified version of game symbols, such as {T} and {W}. These modified symbols should be treated as the standard symbols during play.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Lucas Firmino
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
For many playtest cards, you’ll need to make a generous assumption that basic game rules would be updated to allow them to work. The Mystery Booster 2 Playtest Card Notes section (reproduced here in individual Gatherer rulings) provides guidance for fitting these cards into the existing rules structure.
Emblem isn’t a card type. (Essence of Ajani is still a card, though.)
It doesn’t matter who controlled an emblem spell as it resolved; once it’s put into the command zone, the emblem’s owner controls its abilities.
