Two demonstrations in one: Max PP glitch and the power of TM23 (Pokémon Red):

With at least the TM23 (DF) glitch move, there is a glitch where the total PPs are not constant. I don't know why. It may be 4 at first, but when you heal it changes to 18. In the first case, the Pokémon Center restores its PP to 4, but since the new max PP is 18, it isn't fully restored per se. When you heal again, the nurse will restore the PP to 18, but the new max PP is 4 again, so you have 18/4 PP.

I cheated to get this PkMnaPkMnゥ ♂ fPkMnk (D8) to save time, but no cheats were used to interfere with the max PP (note I did use a cheat to overwrite a move though, so Ice Beam says 24/16 at first).

This glitch helps TM23, learned by D8 at level 86, which is apparently a 255 base power attack with 33% accuracy that also drains damage. It is a Special move (in theory, absolutely no glitch type moves are physical, because all types after Ghost (hex: 08) are Special. I demonstrate how much stronger it can be than Ice Beam (95 base power) against a Mewtwo (note that other things like the variable damage can interfere with this test), and it almost one hit KOd it. As a 255 base power move, I was expecting it to be even stronger though. I guess the low accuracy just makes it not worth it in link battle, but using an X Accuracy, you can make sure that it always hits.