I must say, I have been trying to figure this out since I first played the game in 1995..

What exactly does the soul of zinglon special ability do?

It unleashes this awesome beam attack that goes vertically above and below your ship. Just press primary fire when the little light in the upper corner next to the special ability symbol is lit.

Yes, I know that.

But the beam doesn't appear to DO anything.

Yes, but the damage is worthless on higher difficulty. Only the repulsor and the attractor retain their usefulness in my humble opinion.

That would explain it then.

I haven't played the game on anything less than Hard since about 1998.

Also, Ice Beam is pretty damn great on any difficulty - no shots from the enemy equals less pain.

You should try playing it on Hard difficulty or higher. On Easy or Normal difficulty, you get a different Savara in Episode 1, and you cannot fully complete Episode 3.