Reaper from the Abyss — ruling 1

The morbid ability is mandatory. If you control the only non-Demon creature when the ability triggers, you must choose it as the target.

Reaper from the Abyss : règles, fonctionnement et interactions (MTG)

Reaper from the Abyss 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 Morbid — At the beginning of each end step, if a creature died this turn, destroy target non-Demon creature.

How it works : Reaper from the Abyss

Original English text — Wizards of the Coast / Scryfall

#1September 22, 2011· Wizards of the Coast
The morbid ability is mandatory. If you control the only non-Demon creature when the ability triggers, you must choose it as the target.
No other card is named in this ruling.