Here's a nice one I found posted on another forum:
ChronotronIt's a nice little puzzle where each level requires you to go back in time to the beginning of the puzzle and work with your previous self (or selves) to solve it *without* causing a paradox.
In each level, you need to collect a time circuit for your time machine. Let's say the circuit is behind a door activated by a hot switch. You start by standing on the switch for a few seconds, then go back to your time machine. The puzzle begins again, with your previous self repeating the actions you just did, so while he's holding the door open, you have to grab the circuit and then come out before your old self leaves the switch to enter the time capsule. You then end the level by entering the capsule yourself, since every versions of you need to exit to prevent a paradox. It's really neat and not at all easy, especially in the later levels.
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"With the first link, the chain is forged. The first speech censored, the first thought forbidden, the first freedom denied, chains us all irrevocably." [...] The first time any man's freedom is trodden on, we're all damaged. - Captain Jean-Luc Picard
Current projects:
(Gen), Sonic The Hedgehog (Gen), Sonic CD (Sega CD), Mega Man V (GB), Mega Man Zero (GBA), Battletoads (NES), etc