I think that game is using an alpha channel for that - but having an alpha channel would be outside the scope of 16 bit hardware, and Tilengine, I would think... the SNES just used blending effects per sprite.
Every time I think of the additive blending effect for the SNES, I think of the giant skull in Super Castlevania. https://youtu.be/P0D_H3iX7wQ?t=1133 But I know they must have used it for light sources like in your screenshot.
Every time I think of the additive blending effect for the SNES, I think of the giant skull in Super Castlevania. https://youtu.be/P0D_H3iX7wQ?t=1133 But I know they must have used it for light sources like in your screenshot.