Can I make a transparency mask not with the background, but with a lower layer instead?

I have an isometric wall I wish to punch a hole in but I wish all layers below the wall layer to be visible, the hole itself having the shape of an invisible sprite... As far as i see blend modes get me the results I need but only blend with the background. I need to have other layers visible as well. Is this possible guys?

Cheers!

I'm not sure it's possible. You need to place the mask sprite on the same layer with the wall, and set "Force own textures=yes" in layer properties.

Thanks, this actually works... I was 100% certain I had tried this particular combination - yet I obviously hadn't.