In case rosh havent thought of this already... A multistage Baskerville mode like Man from Beyond, in which a hound figure is lighted with a spotlight, but in the final stage of the mode, the playfield lights go out, and the spot switches to a black light and we see the hound glowing green while we play the ball in the dark, with maybe some limited moving spots of light simulating holmes' lantern.

Another idea -- we have to hit different targets to break Napoleon busts to find the hidden item, which could be in any one of them, similar to smashing the idols on TOTAN.