Slasher of Veils
This creature from another dimension is both death and beyond death. Unconquerable on this domain, his evil can only be subdued for a short time before he returns.
This daemon is from another dimension. It has immense powers and can only be banished once weakened, never killed. Players can choose to summon it at the bottom of the Abyss. If they're defeated, it will rampage in the lower levels until it's pushed back to its portal. During that time, some creatures of the Abyss will go into hiding while others will rally with the daemon. Every hour that passes with it on the loose extends its influence. If the Slasher is not summoned by players for a week, it will randomly spawn at the bottom of the Abyss. Players would be wise to summon it in a more contained location. The Slasher creates a dimensional rift where it spawns. The closer it is to the rift, the stronger it will be and inversely. If the players defeat it, it will flee into the rift in order to restore itself, closing it in the process. If the Slasher is too far from the rift and about to be defeated, it will create a portal that takes it closer to the rift to rejuvenate itself. It must be defeated in this area before the players can push it back.
