Upon chatting with Charak, I've realized I've made a slight error in balancing as it is a GK monster hence it would have 500 attack.

Name: Rare Hunter Ghoul
Level/rank: 2
Attribute: Dark
Monster Type(s): Spellcaster
Effect: Cannot be destroyed by battle. When an opponent's monster declares a direct attack while this card is in your Graveyard while "Necrovalley" is on the field: You can Special Summon this card from your Graveyard in face-up Attack Position, and if you do add 1 "Gravekeeper's" Monster from your graveyard to your hand. This effect cannot be negated by the effect of "Necrovalley". During the next standby phase of the turn you used this effect: shuffle this card into the deck.
ATK/DEF 0/0

Edited the effects a bit.