I'm pretty sure the disappearing blade trick is a simple misdirection ploy. It helps keep an opponent from getting a read on his length and reach, as well as lightening the physical load on his wielder.
Outside that... I'd actually have to say, fighting him alone might be the better choice. Even if he does go weapon, a scythe isn't exactly Sid's weapon of choice, and there is the off choice that the 'obvious' choice is in fact so obvious as to become the less obvious choice. Everyone expects the trick, I mean it's so blatant it's hard to actually believe it is a trick.
Ether way, you're in for 'fun times'. I wish you luck.
Also we had a moment there where we saw from other people's POV. Not to much learned. Fran is effectively a testube baby (The details are a bit more macabre, but it doesn't really matter), her father seems to acknowledge her status as his daughter though. As a note, she was explicitly trained and couched towards being a doctor first. Her being a mister apparently was an independent choice. Not sure how useful this information will be for you, but it might be an in socially if she's feeling down about something.
Nagisa's previous superior Keel Lorenz apparently didn't want him here, or at the least put up a good fight about not 'letting him go'. This could be a good thing, or a bad thing. Again, unsure how useful it is, but more information for you.
Claudia is from one of the European divisions, with a mention to a Doctor Gia being highlighted... This could be trouble as it ups the probability of her having some analogue to the ValkyrieTrace system (the thing that drives her berserk and kills her). They are also under the assumption she's a muti form weapon, rather then powered armor (I'm still leaning to the later).
This is all the information I can at the current moment disclose of use to you. Sorry it's not to much.
Oh wait. One last bit of advice. It's not much, but about scythes in general. A scythe is a momentum based weapon, so you can normally see the lineup of an attack coming a mile away, but if it hits, it'll hit like a dump truck. Also be wary of the wide striking range it'll offer. No matter how unconventional, a pole arm will always have the reach advantage on hand to hand techniques. However, when you combine these factors, with that disappearing blade trick, you're going to have to keep a very close eye on the weapon itself, rather then footwork (which I know can be rather debilitating), because Sid will likely be able to change the weight (and hence speed) of a swing on the drop of a hat.
I'd recommend going for the legs when you can. Scythe techniques while striking primarily from the hips to upper body, rely heavily on having a proper footing, because they're basically exclusively heavy blows. If you can keep them off balance, then they will become even more debilitated then most spear fighters.