You pay all costs for the instant or sorcery spell you cast this way.

As Your Wish Is My Command resolves, you find an instant or sorcery spell from among cards in your sideboard and choose whether or not to cast it. If you do, you cast it as part of the resolution of Your Wish Is My Command. You can’t wait to cast it later in the turn. Timing restrictions based on the card’s type are ignored.

The additional mode you choose can’t be the same as one you’re already choosing with that spell unless that spell allows you to choose the same mode more than once.

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!).

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.

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.