Illusory Demon — ruling 1

If you cast a spell, the spell goes on the stack, then Illusory Demon’s triggered ability goes on the stack on top of it. The triggered ability will resolve (and you’ll sacrifice Illusory Demon) before the spell resolves.

Illusory Demon : règles, fonctionnement et interactions (MTG)

Illusory Demon 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

Flying When you cast a spell, sacrifice this creature.

How it works : Illusory Demon

Original English text — Wizards of the Coast / Scryfall

#1May 1, 2009· Wizards of the Coast
If you cast a spell, the spell goes on the stack, then Illusory Demon’s triggered ability goes on the stack on top of it. The triggered ability will resolve (and you’ll sacrifice Illusory Demon) before the spell resolves.
No other card is named in this ruling.