A glass cannon is a highly offense based Pokemon with a high speed stat. The point is that it hits like a truck, but can barely take any hits. This, however, does not matter if you out speed your target and get a One-hit K.O.
For example, a good statspread would be 100 HP, 120 Attack, 45 Defense, 90 Sp. Attack, 45 Sp. Defense, 100 Speed. This is usually not the case, but this would be ideal.
Some Pokemon that are glass cannons are:
Sharpedo, Alakazam, Kilowattrel, Barraskewda, Pheromosa, Archeops, Aerodactyl, Gengar, and Galarian Darmanitan (In both forms, but especially zen mode.)
Using a glass cannon is not really much of a boost in a playthrough, as most players will out level and most likely outspeed their opponents. However, in most VGC formats, the level is set to 50, which makes glass cannons much more useful. It's one of the reasons mons like Dragapult, Darmanitan, Alakazam, and Barraskewda have seen much competitive use at one time or another.
Hope this can help you.
Source for some of the examples: https://gamerant.com/pokemon-best-glass-cannons/
Everything else: My own experience, through watching worlds since 2019, and having beaten Run & Bun multiple times, therefore having to learn competitively viable mons to actually beat it.
