Well, we have two camps of people drawing weapons.

The camp of people that make weapons that could conceivably be used, and the camp of people who go full anime and make them enormous.

Oversized_weapon would be for the latter.

+1, though you'll have trouble with people mixing up the two, ("It's not too big!"), or justifying it ("well, he's a big character, it make sense that he uses a really big weapon!" ) or whatnot.

Maybe instead of 'oversized' something like over_the_top_weapon or ridiculous_weapon

For weapons that are 'why the hell would you even make that' .. y'know "well, I guess that's kinda a sword"...

like on the middle character here: post #1399238

Not sure about this, mostly because historical swords tend to get called 'ridiculously big' these days.

I think I've posted this before, but... http://farm5.static.flickr.com/4027/4423063256_c5e0181169.jpg and https://i.imgur.com/VFUIHro.jpg

By the way, the second one only weights 14.5lbs, so nowhere near as ridiculous as it seems. And it's a parade sword, zweihanders usually weighted less than half of that..

And here's some bastard swords: https://www.youtube.com/watch?v=iF_kxAqS_8k

Fair... people do need to make a judgement call on that and some people.... won't.

Maybe something like massive_melee_weapon that makes it a bit more clear? I mean the guy with the head-taller-than-him sword will still get tagged with it, but...

Massive_melee_weapon?
Fantasy_weapon? <--could be used for the 'what even IS that' weapons like in my picture. But maybe this should be a tag of it's own.
Anime_weapon?
Physics_defying_weapon?
my_sword_is_too_big? :D

oversized_weapon is already a tag.