Pyro Boy fired 2500 rockets simultaneously at the 2014 Western Winter Blast in Arizona. It's apparently a really challenging proposition, and it's obviously a lot of goddamn fun too.
With an effect like this, it's really hard to get all of the rockets to launch at once. Some of them jam, some of them fall apart, some of them explode on the launch pad. All in all, we only had 30 rockets that did not light, which is absolutely amazing.