[Unless they're in a cave, basically every Netherworld resident will notice the sky being blotted out for a short period of time. Strange things happen to the environment as gravitational forces go haywire. Eventually, an epically loud voice booms, audible to all but the deaf.]
Ow! I stubbed my tail... What's this? Oh, a planet! Sorry about that! Lucky you had that barrier.
Better be getting on my way!
[The impossibly large Overlord slithers away through space, restoring peace and prosperity to the--well, no longer actively detracting from peace and prosperity in the Netherworld.]