They are in the Retroarch Overlays Folder with a template to make game specific overlays.
Megadrive is for 1x resolution of 320x224 which you might have to set. The core config had it full + wide screen on my 3DS.
Turbo Duo is 256x224. I don't use that core so I don't know what the default is.
Megadrive is for 1x resolution of 320x224 which you might have to set. The core config had it full + wide screen on my 3DS.
Turbo Duo is 256x224. I don't use that core so I don't know what the default is.