Descent into Madness — ruling 1

For each despair counter on Descent into Madness, you’ll exile a permanent you control or exile a card from your hand, not both.

Descent into Madness — ruling 2

First 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.

Descent into Madness — ruling 3

If 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.

Descent into Madness — ruling 4

If 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.

Descent into Madness : règles, fonctionnement et interactions (MTG)

Descent into Madness is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

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.

How it works : Descent into Madness

Original English text — Wizards of the Coast / Scryfall

#1May 1, 2012· Wizards of the Coast
For each despair counter on Descent into Madness, you’ll exile a permanent you control or exile a card from your hand, not both.
No other card is named in this ruling.
#2May 1, 2012· Wizards of the Coast
First 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.
No other card is named in this ruling.
#3May 1, 2012· Wizards of the Coast
If 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.
No other card is named in this ruling.
#4May 1, 2012· Wizards of the Coast
If 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.
No other card is named in this ruling.