Number 51 can be done without command blocks. Just gotta use piston feed tapes. The piston noises will even help sell the illusion of you being the one that moves.
One of my favorite, long duration pranks is to put glass panes on someone's beacon beam all the way up to build limit. As long as you match the original color, you cannot see them unless you stick your head in the beam. For some reason, people have an occasional desire to fly straight through beacon beams with their elytra. It may take weeks or months for it to be found. The discovery is typically quite abrupt.
14:51 the reason they removed candles and everything else was because they were unfinished. maybe actually read it? And when they were added back, its because they were finished.