I am not impressed by the sample Elder Evils. Each has glaring weaknesses and considering that they want to destroy the world are much too weak. They could never stand against the inhabitants of the world (Great Wyrms, etc.).
But when the Elder Evils would be so strong so that they would actually hard to fend of the PCs would have no chance. Thats why such "World destroying monsters" don't work.
The signs, at least the one of the Atropus, is also not very well thought out. It raises undead. But as those undead are mindless and uncontrolled they are no threat to anyone except those who rise inside or near a city. When you manage to fend those off and to clear the area you "made it" as the other undead in the wilderness won't bother you if you leave them alone. And flying adventurers can destroy those undead easily so after taking care of the sign the undead problem can be resolved much easier than it was probably intended to be.
But when the Elder Evils would be so strong so that they would actually hard to fend of the PCs would have no chance. Thats why such "World destroying monsters" don't work.
The signs, at least the one of the Atropus, is also not very well thought out. It raises undead. But as those undead are mindless and uncontrolled they are no threat to anyone except those who rise inside or near a city. When you manage to fend those off and to clear the area you "made it" as the other undead in the wilderness won't bother you if you leave them alone. And flying adventurers can destroy those undead easily so after taking care of the sign the undead problem can be resolved much easier than it was probably intended to be.