Sprite problem

I added a sprite and I have a black square around it. I can see the sprite this way, but when I add effect "additive", sprite isnt visible in preview. Whats the problem and how can I remove black square?

Additive makes all black pixels invisible, that's what the effect is supposed to do. It "adds" the color plus the background. black is defined as 0.

0 + background gives you background, hence, invisible.