For my tastes, as guidelines I think are worth sticking to, a keyword mechanic needs to be doing offloading in the rules text that makes things more convenient , it needs to have human-understandable reminder text that isnt just the rules text written out, and it needs to be something that other things can usefully reference
Backstory: Mewtwo was created by scientists using the DNA of Mew, another legendary Pokmon, making it a clone
Omen is a spell type, a subtype seen on instants and sorceries, attached to permanent cards
Artifact Color tag templates(None) Ichor Wellspring When this artifact enters or is put into a graveyard from the battlefield, draw a card
It is also a March of the Machine Sealed event but this time in best-of-three matches
This effect can be used offensively, getting rid of a strong creature to hopefully replace it with a much weaker one