REDU format ruling
Gravekeeper's Chief

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)You can only control 1 face-up "Gravekeeper's Chief". Your GY is unaffected by "Necrovalley". When this card is Tribute Summoned: You can target 1 "Gravekeeper's" monster in your GY; Special Summon that target.
Rulings
- You can use the effect of Gravekeeper’s Chief to Special Summon the same monster you Tributed to Summon Gravekeeper’s Chief.
- If you Set, Flip Summon, or Special Summon Gravekeeper’s Chief, its Special Summoning effect is not activated.
- If you have Gravekeeper’s Chief and Necrovalley on the field, you can use Monster Reborn, Premature Burial, Call of the Haunted, etc. to revive monsters from your GY. Also, if you have Gravekeeper's Chief on the field, your opponent can use Monster Reborn on monsters in your GY.
- You cannot activate The Shallow Grave while Necrovalley is active, even if you control Gravekeeper’s Chief, because your opponent cannot Special Summon a monster from his GY.
- If Necrovalley is on the field, and both players control a Gravekeeper’s Chief, then the Flip Effect of Fiber Jar can resolve normally, but if neither, or only 1, player has Gravekeeper’s Chief, then the Flip Effect of Fiber Jar disappears.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.