It makes sense that Brain Gain looks like a surge of electricity, as it is made from thoughts, and thoughts are based on electrical signals in the brain.
The launcher breaks when Three is sent out in "Three Things Good", and this just happens to occur moments before Four could go out. This is either one of two things: one, the Shape Japer's mucked around with the launcher, or two, Four was supposed to have gone first in order for the launcher to work in the first place.
So it takes a while for Numberjacks to be launched out and landed, but the problems in "Seven Wonders" started happening shortly after Seven is out of sight. Did the Puzzler really catch her that quickly?
In "Boxing Day", why didn't Six knock over one side of the box first, then get rid of the whole thing with Brain Gain? The Shape Japer is nearby, and the sides of the box are too tall to jump over, so why not try to escape first instead of putting yourself in a position where you're stuck in an open box and vulnerable to your enemy?
In "The Dreaded Lurgi", One, Two, and the older Numberjacks are not seen. Is it possible that they or at least one or some of them had the lurgi and that's where Four and Six got it from?
In "Seaside Adventure", Spooky is shown to be able to bat the brain-gain away from it's target. What if she did this in "Time Trouble" when Five was about to fall off the edge? She would have been seriously hurt.
The Puzzler trapping the Numberjacks in bubbles becomes more horrifying when you realise that A.) He's willing to keep them in there forever if no one solves his puzzles, and B.) The Numberjacks' numbers correspond to their ages (see "Into the Teens" and the fact that Zero and One are basically babies). So the Puzzler is willing to trap children for eternity. Four Eyes, Zero Soul indeed.
In "Off Colour", Spooky Spoon briefly makes Four cease to exist, all because she thought his bright colour would make her look boring. Does this mean she can get rid of the Numberjacks once and for all?
In "Going Wrong, Going Long", Four is being launched and Three can't find a four for him to land on, so they have Agent 16 make the boy write one. Three and Six have urgency in their voices, claim that Four is "running out of energy", and when they're telling 16 to make the boy write the four, Six prefixes the command with "Quick!" and refers to them needing an "emergency" number. Add this to the fact that the show's official YouTube channel has a video explaining how the launcher works and that process where they turn into mist is referred to as being particulated, this could imply that if the boy hadn't written the number, Four would've fallen apart at the subatomic level.
One scenario Five imagines in "One More Time" is a bird flying over the bridge One is under and getting cloned over and over again. This means that One can not only create life, but do it enough times to cause overpopulation.
On the lighter side, this power would work wonders for endangered species.
