The value of X is determined only once, as Flavor Disaster’s second ability resolves.

If Flavor Disaster is no longer on the battlefield when its second ability resolves, use its power as it last existed on the battlefield to determine the value of X.

Negamorph is a variant of the morph ability. A negamorph ability lets you cast a card face down by paying {3} and announcing that you are casting it face down using a morph ability. Any time you have priority, you can turn a face-down permanent with negamorph face up by paying its negamorph cost.

The face-down spell has no mana cost and has a mana value of 0. When you cast a face-down spell, put it on the stack face down so no other player knows what it is, and pay {3} to cast it. This is an alternative cost.

The creature spell is a 2/2 creature spell that has no name, mana cost, or creature types. The resulting creature is a 2/2 creature that has no name, mana cost, or creature types. Both the spell and the resulting creature are colorless and have a mana value of 0. Other effects that apply to the spell or creature can still grant it any characteristics it doesn’t have or change the characteristics it does have.

Any time you have priority, you may turn the face-down creature face up by revealing what its negamorph cost is and paying that cost. This is a special action. It doesn’t use the stack and can’t be responded to. Only a face-down permanent can be turned face up this way; a face-down spell cannot.

As a permanent with negamorph is turned face up, put a -1/-1 counter on it if its negamorph cost was paid to turn it face up. If it’s turned face up in any other way than paying its negamorph cost, you won’t put a -1/-1 counter on it.

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.