Probably a stage hazard, which I'm fine with. Just play FD if you don't want stage hazards.
Nothing abnormal about it. The majority of the Nintendo character's stages have gimmicks too. What makes you think they are targeting third party stages only? The most popular stages without gimmicks (FD & Battlefield) aren't related to any specific franchise.
What is it with third party stages having weird gimmicks? Shadow Moses Island has those destructible walls that make horizontal KOs difficult. Trying to KO others with Diddy Kong is awful there. Green Hill Zone has the destructible ground and the checkpoint pole, which is annoying to maneuver around. Both have walk-off edges, so they're a chain-grabber's paradise. And now Wily's Castle has the Yellow Devil to contend with. If Pac-Man is in, his stage will probably have the ghosts running around, causing mayhem. Can we please have a gimmick-less third party stage, Sakurai?
Nothing abnormal about it. The majority of the Nintendo character's stages have gimmicks too. What makes you think they are targeting third party stages only? The most popular stages without gimmicks (FD & Battlefield) aren't related to any specific franchise.