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.