Normally, playing a land can only be done as a sorcery, but the madness trigger circumvents that timing restriction, allowing you to play the land even if it’s not your main phase and even if the stack is not empty. However, you can still only play a land during your turn and only if you have an available land play remaining.

If you discard a card with madness, you discard it into exile instead of into your graveyard. When you do, you can either play it from exile for its madness cost or put it into your graveyard.

Cards are discarded in a Magic game only from a player’s hand. Effects that put cards into a player’s graveyard from anywhere else do not cause those cards to be discarded.

Madness works independently of why you’re discarding the card. You could discard it to pay a cost, because a spell or ability tells you to, or because you have too many cards in your hand during your cleanup step. You can’t discard a card with madness just because you want to, though.

A card with madness that’s discarded counts as having been discarded even though it’s put into exile rather than a graveyard. If it was discarded to pay a cost, that cost is still paid. Abilities that trigger when a card is discarded will still trigger.

If you choose not to play a card with madness when the madness triggered ability resolves, it’s put into your graveyard. Madness doesn’t give you another chance to play it later.

If you discard a card with madness to pay the cost of a spell or activated ability, that card’s madness triggered ability will resolve before the spell or ability the discard paid for.

If you discard a card with madness while a spell or ability is resolving, it moves immediately to exile. Continue resolving that spell or ability, noting that the card you discarded is not in your graveyard at this time. Its madness triggered ability will be placed onto the stack once that spell or ability has completely resolved.

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.