When building a GK deck I never run terraforming. You can easily enough search necrovalley using Gravekeeper's Commandant. Also Commandant is useful even if you have necrovally, because it is another monster that the deck needs. Without him the deck only has a couple other playable monsters (Spy, Decedent, and Recruiter). If you played terraforming it will be a dead card to often. Also its a very bad draw.
Obviously this card stops loads of graveyard action, so BLS is dead and DAD can't use it's effect.
As I ave in my GK deck topic, I use this card with solidarity and EEV. EEV, or Eradicator Epidemic Virus is an amazing card against Prophecy. You tribute a Dark monster (Unfortunately you can't use Commandant, he's Earth) with 2500 or more attack and call spells or traps. Look at your opponents hand, spell and trap cards and cards they draw until the third standby phase after activation, and destroy all of the type of cards you called ( call spells against prophecy). It basically gives you 3 turns to win. Also if you don't get it off, using solidarity in a GK deck makes most of your monsters Huge beaters. Your opponent will usually have to use loads of their cards trying to get rid of a single recruiter!
Malefics are quite a boost to this deck. Beacuse when this deck was released, there weren't any synchro or xyz, so you have a lot of deck space. And malefics are quite a boost in attack(A cyber seals the game). Also the master key beetle+Safe zone can be easily summoned with 2 spy.
Important rulings:
If a card in the graveyard banishes itself, it cannot be used when necrovalley is in play.
If a card in the graveyard adds itself to the hand or deck, it can be used when necrovalley is in play.
If a card can special summon itself from the graveyard (Ex. Plaguespreader Zombie) it will work.
Anyway, I like to run more monsters such as Guard, Assailant and Visionary, but I might cut those non-essential cards! Hope I helped!!
Necrovalley:
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