Teferi, Druid of Argoth

While you control Teferi, you may exile creature cards in your hand with suspend any time you could cast an instant.

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.

Teferi’s last ability means that in order for an opponent to cast a spell, it must be that opponent’s turn, during a main phase, and the stack must be empty. This is true even if a rule or effect allows a sorcery to be cast at another time.

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.

If an effect allows an opponent to cast spells any time they could cast an instant (for example, if your opponent controls Teferi, Mage of Zhalfir), the restriction of Teferi’s last ability takes precedence over that permission.

If a spell on the stack has split second while you control Teferi, you can’t suspend creature cards since split second stops you from casting them, even though suspending them is a special action.