How'd they did the effect of Zane taking the flare to the face?

Can't say for sure, but my guess is that he something in his mouth that produced mist and emitted a red light, and there was something on the back of his head that made the explosion effect. Again, it's just a guess.

I strongly suspect it was hand drawn animation rotoscoped onto the master shot. The flare effect was achieved simply through overexposing the animation layer. The same technique was used to create the shimmering light saber effect in Star Wars.