Cheapest priced copy (Avacyn Restored): $0.99 at Card Kingdom, near mint, their price list as of .
Descent into Madness 
Enchantment · Mythic · Avacyn Restored · #97
At the beginning of your upkeep, put a despair counter on this enchantment, then each player exiles X permanents they control and/or cards from their hand, where X is the number of despair counters on this enchantment.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.99 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Avacyn Restored | 97 | Mythic | $0.99 | $1.99 |
4 rulings from Wizards of the Coast
- 1 May 2012First you choose the permanents and/or cards from your hand that will be exiled. Then each other player in turn order does the same. Then all the chosen permanents and cards are exiled simultaneously. Players who choose after you will know what permanents you’ll be exiling when they choose. They’ll know how many cards you’ll be exiling from your hand, but they won’t see those cards.
- 1 May 2012If Descent into Madness isn’t on the battlefield when its ability resolves, use the number of counters on it when it left the battlefield to determine how many permanents and/or cards from hands to exile.
- 1 May 2012If there are more counters on Descent into Madness than the total number of permanents you control plus the number of cards in your hand, you’ll exile all permanents you control (including Descent into Madness) and all cards from your hand.
- 1 May 2012For each despair counter on Descent into Madness, you’ll exile a permanent you control or exile a card from your hand, not both.