When monsters in the Graveyard are removed from play, remove monsters on your side of the field from play as substitutes. This card remains active until the end of the turn that it is activated. The substitutes remain removed from play.
Rulings
Individual Card FAQs
During the turn that "Spirit Elimination" is activated; all monsters removed from play must be from your side of the field. This means that you cannot activated "Soul Release" and remove two monsters from your side of the field and three from your Graveyard.
Any conditions set on the Monster Cards that would be removed from the Graveyard must still be fulfilled on the Monsters removed from your side of the field. For example, to Special Summon "Dark Necrofear" you must remove 3 Fiend-Type Monsters from your side of the field.
You can activate "Spirit Elimination" while "Necrovalley" is active.