I disagree.
As with most obscure "junk" or "joke" items in Final Fantasy, there is indeed a valid use for even this weird sword, even if it's a niche use...
In Final Fantasy V, "Excalipur" (or Excalipoor depending on your version) always does one damage. What is not immediately evident is that it ALWAYS hits.
Always. This means that even with 255 evade anyone getting hit with this thing cannot dodge the blow and said blow cannot miss.
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So, what do we do with this? Remember those gray squirrel-like things called "Skull Eaters" that first appear in the Jacole (or Jachol) Cave? The ones that are incredibly hard to hit and who will totally wreck the unsuspecting lowbie party? Did you know those things only have 1 hitpoint? Did you also know they're worth quite a lot of AP? 5-10 actually, depending on how many monsters are in the formation. IIRC they also split into multiple copies when hit with magic but since they hit rather hard this might not be a smart move.
Anyway. The Excalipur is the perfect tool to farming those little gray bags of ability points. Smack one with it and it invariably does the one damage it's supposed to and kills the enemy in swift order since their hpmax is 1.
In my view this is a valid use for Excalipur that you should make use of before you hurl it at Exdeath's face for 9999 damage.
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Another glitchy use for Exalipur is to use it in combination with Goblin Punch. The coding that makes the sword (and a few simiar weapons) do a fixed amount of damage (in this case, one) is bugged when you use Goblin Punch and it instead uses the "full" attack power of the sword. I do believe that THIS particular use of the sword has been patched out in the later versions of the game, but it does work in the original SNES/Super Famicon version. The same buggy code still works with "throw" though, so feel free to chuck this at an enemy of your choice when you're done farming squirrels with it.