Super Mario World One Mind
This is a ROMhack of Super Mario World that switches who is in control of playing mid-level. In slow mode, the switch can occur every 3-8 seconds. There will be a warning sound before each switch. In fast mode, the switch happens every second. You can switch modes by holding Start and Select while the overworld is loading at any time. You'll know you're in fast mode when Mario shows up blue on the overworld.
There are a few versions of this ROMhack for different numbers of players:
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