Add a hud message explaining the effect of the Helm of the Dead.

[Kanta]

A simple message like "This helm protects you from undead foes. (25%)" would work.
Changing the description wouldn't hurt either.

 

[Kanta]

Not a hud message, but an event window message, my bad.

 

[Thothie]

Modified description (and created my 100th "//duplicate in ALP2020" tag, hopefully I catch all these).