See where Essence of Ajani is available worldwide and at your local stores
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 and . These modified symbols should be treated as the standard symbols during play.
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.