My favorite ideas are generally those that are simple but have lots of puzzle potential, so out of these eight, my favorite is the reverse lockholes, though I think they could use a better sprite than “pink/cyan lockholes”; perhaps the lockholes would still be their regular color, but with a little plus sign inside the circle part of the lockhole? The plus would be the opposite color of the lockhole: white for the black positive locks, black for the white negative locks.