I think the dice and the ray of light are made to spice up the game. The Ray of Light wears off at a rate for -1 to -8 per battle. So I guess you may want to take it off when not fighting undead and demons.
I used the crown before and it worked. Unless something bugged in the english version of KBAP, it shuld be working.
The Silver rapier takes effect only against undead. Its bonus is indeed invisible as it is, because it does not affect the unit in general. However, the damage increase is noticeable.
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