An update to a preexisting calc, the speed shown here for Power Stars. Originally this was scaled to World 5 because it features a galaxy cluster in the background. However, these worlds are also directly called universes in the Japanese games, so time to calc this.

As you can see, worlds are called universes. Screenshot gotten from the Super Mario Wiki

All time values will be gotten from here.

1st version - traveling one universe (World 5) in 0.3 seconds

93.016 billion lightyears = 8.80024376 * 10^26 meters

(8.80024376 * 10^26 meters) / 0.3 seconds

2.9334145867 * 10^27 m/s or 6.5618724255 * 10^27 mph

9,784,817,824,400,000,000c (9.78 quintillion c)

2nd version - traveling seven universes in 2.07 seconds

93.016 * 7 universes = 651.112 billion lightyears = 6.160170632 * 10^27 meters

6.160170632 * 10^27 meters / 2.07 seconds

2.9759278415 * 10^27 m/s or 6.6569720259 * 10^27 mph

9,926,626,778,400,000,000c (9.93 quintillion c)

Quite the upgrade.

Obviously this scales for reasons characters already scale to Power Stars. Mario and Luigi regularly fight and defeat bosses amped or powered by Power Stars like King Bob-omb, Dino Piranha, and King Kaliente.