OMG the lock mechanism on the Lego NES! The way it catches and releases!!!! When it came together and I realized what I'd just built was one of the most magical moments
Lego Robot Claw Mechanism - Michael Normand - Robot Mechanism Design - UT Austin Wikis
LEGO MOC Periodically Reversing Mechanism #3 by 2in1 | Rebrickable - Build with LEGO