It's very simple.
You put this somewhere in your script:


material bloodeffect
{
effect="
technique burn
{
pass p0
{
AlphaBlendEnable=true;
//ColorOp[0.n] = Subtract;
srcblend=destcolor;
destblend=invsrcalpha;
}
}";
}



and add this action to the sprite:

action bloodsprite
{
my.material = bloodeffect;
}