I think "hidden" is the version of the gene (allele) that combines with lesser to make platy. It's perhaps the oddest member of this complex in that both the hets with normal and even the homozygous hidden apparently look normal. It's just that when combined with lesser, hidden makes platy.

I understand that special is a visual morph (and another allele of this complex) and when combined with mojave makes crystal. Also unlike hidden the homozygous special is a stunning morph.

Mystic and phantom might be the same and are in this complex. Phantom with lesser makes a leucistic (karma) but most of the other combos so far involving these two seem to make darker animals.