Dark Matter is an interesting concept, yes. Can't think of any uses at the moment though...
Tritium is basically SING when it explodes(Set its life to 255, then back to 1)
Atom mode is an entirely different game. Try waiting for a while, we'll finish with the JavaPowder base(we'll still do it obv) and begin on an atom simulator thing.
Magnets would need an entire "layer"(you know, like pressure or velocity or newtonian gravity) to work. That will slow the entire game down, but it's possible.