The text says:
Negate the effects of Effect Monsters destroyed by battle with Zombie-Type monsters you control.
Doesn't that mean the negation is permanent? Even if the monster leaves the field, in the GY, banished, etc.. it is still negated forever until it is returned to the hand?
It doesn't say until the end of the turn.
Check the asker question.
He even said the keeper didn't get destroyed by battle but his BE instead, while in this case keeper should be activated UNLESS it got destroyed by battle with Hades the past turn, which rendering its effect negated. I suppose this should happen just before solid dragon negate hades.
Revival king Hades wont work if the monster didn't get destroyed to begin with.
Necrovalley kinda semi lock them in spite of how they get into GY.
You just can't compete with Necrovalley.
Anubis might be a better choice, but as a level 6 you cant use it instantly like necrovalley to begin with