So I was wondering if there is a limit to how many Gem can use together at once. Theoretically, it's limitless. But not in practice. Considering fusion requiring all parties to be in the perfect sink; the more gems, there for more clashing personalities, the more unstable it will become. Even Gems of the same type still have minor differences between them, which would eventually build up, forcing the fusion to fail. Having separate individuals with identical personalities to practically impossible. Even if they are clones, who are present at the same events, they will still have different experiences, making differences in their personality. For example, if they are in a fight, one will get hit/hurt more then the other.