Link - Tears of the Kingdom
How it works:
The arm was made of two layers: a black mesh glove overlaid on top of an opaque white glove. The white glove was painted, going from light blue to lime green in luminescent paint.
Foam cutouts painted gold were attached to the black mesh glove with contact cement and inlaid with UV paint to make the glowing lines. Fake acrylic nails were glued to the backside of the fingers of the black mesh glove to give the illusion they were attached to the hand directly.
I created a luminescent nail polish by mixing luminescent powder with clear coat nail polish. The acrylic nails were first painted with the a dark teal (as seen in the game when the arm isn't activated), then coated with a thin layer of the home-made nail polish. This way, the nails would glow white in the dark, but the "unactived" darker color could still be seen when not glowing.