Nightmare Shepherd

Mana cost: {2}{B}{B}
Type: Enchantment Creature — Demon
Power / toughness: 4 / 4
Set: Theros Beyond Death Promos #108s (rare)

Flying
Whenever another nontoken creature you control dies, you may exile it. If you do, create a token that's a copy of that creature, except it's 1/1 and it's a Nightmare in addition to its other types.

Nightmare Shepherd has 6 printings, first in Theros Beyond Death (2020). EDHREC ranks it #4,488 among Commander cards. It appears most in Aminatou, Veil Piercer decks (5,194 on EDHREC). 1 public deck on TCG runs it. It has 7 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: legal
standard: not legal
brawl: legal

Public decks that run Nightmare Shepherd

Miracle Worker - Duskmourn: House of Horror Commander, led by Aminatou, Veil Piercer

Commanders that run Nightmare Shepherd most

Deck counts from EDHREC.

Often played with Nightmare Shepherd

Cards that show up in the same decks on EDHREC.

Rulings

2020-01-24: If the copied creature had {X} in its mana cost, X is considered to be 0.
2020-01-24: If the copied creature was copying something else, then the token enters the battlefield as whatever that creature copied.
2020-01-24: If the token is a copy of a creature whose power and toughness are defined by an ability (usually printed as */* or similar), the token doesn't copy the ability that defines its power and toughness. It remains a 1/1 creature.
2020-01-24: The token copies exactly what was printed on the original creature and nothing else (unless that creature is copying something else; see below). It doesn't copy whether that creature was tapped or untapped, whether it had any counters on it or Auras or Equipment attached to it, or any non-copy effects that had changed its power, toughness, types, color, or so on.
2020-01-24: The token copies the creature as it last existed on the battlefield before it died, not as it existed in the graveyard before it was exiled.
2020-01-24: If something becomes a copy of the token, the copy is also a 1/1 and a Nightmare.
2020-01-24: Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any "as [this creature] enters the battlefield" or "[this creature] enters the battlefield with" abilities of the creature will also work.