Chainer, Dementia Master
Legendary Creature — Human Minion
All Nightmares get +1/+1.
, Pay 3 life: Put target creature card from a graveyard onto the battlefield under your control. That creature is black and is a Nightmare in addition to its other creature types.
When Chainer leaves the battlefield, exile all Nightmares.
Mark Zug
Commander Masters (CMM)
• #144Rulings
The creature put onto the battlefield by Chainer's activated ability is black only, not black in addition to its other colors. It is, however, a Nightmare in addition to its other creature types. As it enters the battlefield, it is already a black Nightmare (and perhaps some other creature types); it doesn't enter and then become a black Nightmare.
(wotc • 2022-12-08)
Rulings
The creature put onto the battlefield by Chainer's activated ability is black only, not black in addition to its other colors. It is, however, a Nightmare in addition to its other creature types. As it enters the battlefield, it is already a black Nightmare (and perhaps some other creature types); it doesn't enter and then become a black Nightmare.
(wotc • 2022-12-08)