mwaetht, ralouf1
The point is it's, a sketchy deck, it's got a single gimmick and no way to defend itself, it's not meant to win, klown420 gets it though.
But to answer the question more directly, The soul catcher isn't needed, it's really just up there as a 30th card, except in one condition, to beat out an early bone wall or hope for a break in dimensional shields, the sparks would feed the wall only, and are not by themselves a kill against a break in dimensional shield chain. You need a lot of something more perm to wipe the wall, or do a kill in a chain break. So it's to feed a set of fractaled vultures just in case. I remember when playing around with this deck when I first built it, I was using boneyards or bonewalls to further take advantage of the death effect, but at the amount of electrum those cost and only getting one death point a turn they can force you to be holding onto a card during the early turns, which means one less spark per fractal in your hand. Which is in most cases the difference between a win and a loss, in the end the only thing that was fast enough and gave a chance at beating some of it's weaknesses was that one soul catcher.
The win draw is:
Basically, on turn 3 you want a vulture and a set of fractal sparks, which would result in 21 damage, and a 7/9 vulture, turn 4 is 28 damage total, turn 5 is another fractal spark of 56 total damage and a 14/15 creature, turn 6 is 70 total damage and turn 7 is another round of fractal sparks for for 106 total damage.
Again a bone wall, a few early quakes, faster deck, or chained dimensional shields or just about any upgraded deck would knock it down.