Dark Souls Remastered | Invading and defeating a Gravelord Servant & disasters vanish

In Dark Souls 1, a world gets infected by a Gravelord Servant when a player in the Gravelord Covenant uses the Eye of Death while in their own world. This curses the worlds of other players who are in the same area and online, causing tough Black Phantom enemies to appear in their game. These phantoms are more powerful versions of regular enemies.

Affected players can see a sign in their world that lets them invade the Gravelord Servant's world to hunt them down and break the curse. The infection ends if the Gravelord Servant dies or leaves the area.

Gravelord Servant
https://darksouls.wiki.fextralife.com/Gravelord+Servant

You can read more about it in this thread:
https://fextralife.com/forums/t1189/quotdisasters-are-gone-after-the-defeat-of-the-gravelord-servantquot-what