For fun:
Throwing sticky resin on mobs to make them stick/stuck on ground or near wall. I think it would be fun like to make stucked mobs field 
or just for retreat plan.
Way of usage:
Maybe gun or just resin balls.
Temporary effect or permament?
What happens when mob dies, will it drops resin ball too? Personally i dont think that we lack of resin, so i think it should be one time use.