Shadow plane - which blend mode?

Hi, I'm trying to create a simple shadow plane to sit beneath my player object. This is just the old-school shadow blob like the old Resident Evil games.

I've tried a dark gray circle on a black background, I've tried a black circle on a white background and neither one will blend to create the effect I want.

I just want the circular shadow to show and not the rest of the texture. The shadow has to be dark coloured. Any adice?

Thanks!