Onyx Mage — ruling 1

Multiple instances of deathtouch on the same creature provide no additional benefit. A creature dealt damage by a creature with multiple instances of deathtouch is destroyed only once.

Onyx Mage : règles, fonctionnement et interactions (MTG)

Onyx Mage 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

: Target creature you control gains deathtouch until end of turn. (Any amount of damage it deals to a creature is enough to destroy it.)

How it works : Onyx Mage

Original English text — Wizards of the Coast / Scryfall

#1September 22, 2011· Wizards of the Coast
Multiple instances of deathtouch on the same creature provide no additional benefit. A creature dealt damage by a creature with multiple instances of deathtouch is destroyed only once.
No other card is named in this ruling.