Cavalcade of Calamity — ruling 1

A creature with power 0 or less can attack, as long as no rule or effect prohibits it from doing so. Many creatures with 0 power have defender, but not all do.

Cavalcade of Calamity — ruling 2

The power of the attacking creature is checked only when the ability triggers. Once it triggers, Cavalcade of Calamity will deal 1 damage to the appropriate player or planeswalker even if the creature’s power changes or the creature leaves the battlefield before the ability resolves.

Cavalcade of Calamity — ruling 3

If multiple creatures you control with power 1 or less attack, Cavalcade of Calamity’s ability will trigger for each of those creatures. Each ability will cause Cavalcade of Calamity to deal 1 damage to the appropriate player or planeswalker.

Cavalcade of Calamity : règles, fonctionnement et interactions (MTG)

Cavalcade of Calamity 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

Whenever a creature you control with power 1 or less attacks, this enchantment deals 1 damage to the player or planeswalker that creature is attacking.

How it works : Cavalcade of Calamity

Original English text — Wizards of the Coast / Scryfall

#1January 25, 2019· Wizards of the Coast
A creature with power 0 or less can attack, as long as no rule or effect prohibits it from doing so. Many creatures with 0 power have defender, but not all do.
No other card is named in this ruling.
#2January 25, 2019· Wizards of the Coast
The power of the attacking creature is checked only when the ability triggers. Once it triggers, Cavalcade of Calamity will deal 1 damage to the appropriate player or planeswalker even if the creature’s power changes or the creature leaves the battlefield before the ability resolves.
No other card is named in this ruling.
#3January 25, 2019· Wizards of the Coast
If multiple creatures you control with power 1 or less attack, Cavalcade of Calamity’s ability will trigger for each of those creatures. Each ability will cause Cavalcade of Calamity to deal 1 damage to the appropriate player or planeswalker.
No other card is named in this ruling.