'Fading' was introduced in the Nemesis and it currently appears on a number of cards: Jolting Merfolk, Parralax Nexus and more.

702.29. Fading

• 702.29a. Fading is a keyword that represents two abilities. "Fading N" means "This permanent enters the battlefield with N fade counters on it" and "At the beginning of your upkeep, remove a fade counter from this permanent. If you can't, sacrifice the permanent."

Translation:

• 702.29a. It's two things. When it enters the battlefield put N counters on it. And then every upkeep after, remove a counter. If there isn't a counter to be removed, sacrifice it.