Honestly? Not much. The scythe isn’t, and never has been a weapon. It can be used as an improvised weapon in a pinch, but, to the best of my knowledge there’s never been a formalized combat style involving one. Real scythes were designed around a simple, horizontal swiping motion to, well, scythe down grain. The blade was on the edge facing the user, meaning to use it as a weapon you would have to strike past your foe and pull towards you. When you’re dealing with grain, that’s useful, when you’re dealing with someone wanting to remove your internal organs, it’s a bad thing.
The only thought on the scythe I can think of would be to treat it like an axe or pick. You could look at some forms of axe combat, particularly the bearded axe, which involves building momentum in a crossing figure eight motion.
For writing a mecha story in general, I would suggest taking a look at the GURPS Mecha book by David Pulver. Like most of the GURPS supplements, it spends a lot of time talking about considerations for world building and how to pace a longer story or series. I’m not an expert, but the material it presents looks solid enough at first glance, and should give you some help with your story. A few caveats: it spends almost no time talking about melee combat in Mecha, and it does assume you have the core GURPS book and Compendium I, though, from a writing standpoint, those aren’t actually necessary.
wetmattos said: I’ve seen, once, a video of a scythe fighter, and according to him the most difficult thing on wielding it is to maintain balance – but it seems viable (even if really risky) enough. Sending the video! youtube.com/watch?v…
That’s actually a pretty good suggestion, at least on a visual level. What you’re seeing there looks like a form of Wushu staff technique.
It’s not a practical way to fight with a scythe, but, given we’re talking about Mecha fighting, it doesn’t need to be.