Original Famicom user here.
First of all thank you for the mapper!

I just gave a brief test to Gimmick! and Batman.
Batman - no issues noticed.
Gimmick! - once, at the end of the stage 1, whole screen got messed up graphics for 1-2 seconds and after that everything went back to normal
Also noticed weird scanlines on some objects (pictures below), but this can be my LCD aswell so not sure if that's normal. They are appearing depending on the movement -
if I'd do a one more step they'd be gone, and back when moved a little bit further.
Sound seems to be fine, I haven't noticed any delays.

