Cosplay masquerade judges will NOT tear you to shreds. In fact, they'll easily recognize your nervousness and they'll probably try to prompt you to get you to talk and ease into the whole judging thing. It's really not as bad as it sounds.
Most anime con judges are very supportive. If they notice anything flawed, they will not criticize you to your face. There may be some critique behind closed doors amongst themselves, but it will be about all contestants, not just you, for the purpose of deciding and ranking awards. They will not get mean with you or criticize unless you actually ask them to point things out or give a critique.
The reason they do pre-judging for craftsmanship is to make the competition more fair. If the judges only judged a costume when seeing it on the stage, it would only be an anime-themed Halloween contest. (And we all know how those go, the best costumes never win!) Pre-judging allows the judges to really see your costume in a personal setting, so they can appreciate it on its own terms and get a better idea of what you did to make it. Some aspects wouldn't be visible from the stage at all, and they wouldn't know what you did during construction without talking to you.
Bring reference images with you. It also helps if you bring a couple construction progress pics if you have them. (At the least, it helps prove you made the costume.) They will WANT to hear you talk.
You can go to judging wearing your costume, or bring it in on a hanger or in a box. I tell people to do whatever shows the costume off better. If you're wearing it, no one will physically nitpick, flip things over, or turn inside out without your permission. Judges understand personal space.
FF9 cosplay? Hit me up!
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