Stick to your guns. Screw cosplay, you have tickets.
Manjoume (Black Thunder ver). Because GX represent, you luffs him to itty-bitty moe pieces and the costume's easy (although the wig would prevent anyone behind from seeing the film. OH RA that wig styling. *cringes*).
Yami Bakura. You have the outfit already. Never mind that there will already be 50 people there dressed as him, he's just awesome like that.
fem!Kaiba. Because if you keep doing it, it might eventually turn out right. And we enjoy seeing your discomfort in PVC stockings. But HOMG that coat ;A; How are you going to do that in time...
Hell Kaiser Ryo, who else? LOOKIT YOUR FACEBOOK PICTURE. You can do a complete outfit in time if you just recruit some adoring fangirls. You have those, right?
Yami no Rowan. (What would that be like? XD)