Soul Spike
This seems to be the card where the most speculation dwells. I think it is imperative people understand the explosive nature behind Storm-based combo decks that can just win at any given time. The Gate runs a good portion of disruption, so keeping an opponent from killing you for a turn or two is an acceptable means to aggressively irritate their strategy early in the game. Let's assume you defeat combo the first game with your proactive discard, and you are ready to proceed to the sideboard.
Against
Ad Nauseam, on the draw, you are looking dead in the water. Combo is an extraordinarily difficult match to deal with on the draw because now you are allowing the player to Brainstorm or cantrip before you have an opportunity to discard the meat of their hand. When they do this, they can go off in a hurry without any problems. Allow me to cite a specific example from my first round, second game match against Bryant Cook at Jupiter Games' Anniversary event:
Bryant ends up "going off" turn two, when I have no way of stopping him at this point. Let me say that again:
No way. Aside from discard, there really is no other way to stun the combo player as you purposely run no acceleration. So, while the combo player is going off, there is a very realistic possibility they will stop at four life or less. The reason for this is due to the inclusion of key cards like Tendrils of Agony, Empty the Warrens, or Ill-Gotten Gains.
Notice the cost of each of those cards.
Storm combo players have a tendency to stop at or near that life total because they fear flipping to their death. I have played countless matches against Bryant where he stops at four or less life. There's no reason not to; they
need those cards in order to kill
you. So once they decide to cast an acceleration spell or a win condition, you respond by killing them. If a Storm player stops at five life and Empties the Warrens, then that is unfortunate. In that case, there is nothing you'd be able to do anyway, because having them create a million Goblins is going to be hard for
anyone to deal with turn two. But, this gives us a legitimate out against them when they do drop to a life total of four or lower and can kill them in response to anything they play.
Remember, you're also gaining four life to potentially cripple them from expending what the have on a storm count of ten or eleven because you gain life as well. Off Ad Nauseam, they are only gaining back what they lost with Tendrils, so recuperating and coming back offensively to kill them is not entirely impossible; I've done it.
The card is also not useless against Zoo; you're giving yourself an opportunity to gain life at a point in the game where losing life becomes more and more dangerous. You're also doing damage at the same time. Spinning Darkness does this (essentially) for free as well, and is a little more reasonable in the cost. You would also want to remove Dark Confidant straight-up for Spinning Darkness against Zoo games two and three. I learned from my match in the Top Four by not siding correctly (I kept Dark Confidant in). Do not keep Dark Confidant in except against Storm with Soul Spike coming in. It is worth taking the risk trying to net more cards while attempting to kill them unknowingly.