They are funny as memes, but beginner DMs might not be able to tell the difference.

I feel the same way about the False Hydra. As a recounted creepypasta it sounds cool. As an actual TTRPG enemy it's unworkable. Either the adventure will be very scripted, because the DM has to pretty much allow you to perceive it, or it will be completely unfair and insufferable, because you'll need to constantly pretend you don't notice it and that you forget things as it decimates the party. It's not a good D&D enemy, it doesn't even fit the rules of D&D well. Mind effect with no saves unless you cover your ears? C'mon...