Will-o-wisps and Maze

[Crothian]

The problem with things that are immune to every spell except such-and-such is that it doesn't take into account new sources.

Sure it does, it's immune to all of them

 

[Warren Okuma]

Maze?

Because Will o Wisps are silly creatures.

 

[Quasqueton]

In the AD&D1 Monster Manual, they are also vulnerable to protection from evil.

Quasqueton

 

[Tonguez]

In some folklore (finnish?) Willowisps were said to mark the site of ancient treasure and they could be stopped by either being trapped with no way out (in a maze?) or by placing a knife in the ground blade pointed up (which they would impale themselves upon.
It is thought that these might be references to ball ligntning (hence the attraction to metalic artifacts) with the knife acting as a lightning rod

Anyway this might explain maze (maybe)

 

[Alzrius]

Clearly this is due to will-o-wisps hating the taste of corn. How else do you explain their vulnerability to maize.

 

[T. Foster]

FWIW, there's no mention of any spell immunity (Maze excepted or otherwise) in the OD&D Will O'Wisp description from Supplement I, so that's purely an AD&Dism.