The Ruinous Powers — ruling 1

You must follow all normal timing rules when casting a spell or playing a land using the permission granted by Ruinous Powers.

The Ruinous Powers — ruling 2

Use the mana value of the spell as it exists on the stack (or last existed on the stack, if it's been removed) to determine how much life is lost. If there is an {X} in that spell's cost, include the value chosen for X to determine its mana value.

The Ruinous Powers : règles, fonctionnement et interactions (MTG)

The Ruinous Powers 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, choose an opponent at random. Exile the top card of that player's library. Until end of turn, you may play that card and you may spend mana as though it were mana of any color to cast it. When you cast a spell this way, its owner loses life equal to its mana value.

How it works : The Ruinous Powers

Original English text — Wizards of the Coast / Scryfall

#1October 7, 2022· Wizards of the Coast
You must follow all normal timing rules when casting a spell or playing a land using the permission granted by Ruinous Powers.
No other card is named in this ruling.
#2October 7, 2022· Wizards of the Coast
Use the mana value of the spell as it exists on the stack (or last existed on the stack, if it's been removed) to determine how much life is lost. If there is an in that spell's cost, include the value chosen for X to determine its mana value.
No other card is named in this ruling.