Level 6-7 (Mario vs. Donkey Kong: Tipping Stars)
From the Super Mario Wiki
The course has sets of Pink Block spaces and Purple Conveyor Rivets, as well as one Circus Kong at the right and one Cannon Kong at the bottom. All four keyless Mini Marios proceed facing the same direction at the top of the course. They soon fall inside a gap, where the Circus Kong throws them back up, but helps them collect a Large Conveyor Pickup. With the acquired Purple Conveyors, the Minis can then be led into the pair of Hammers further to the top, necessary to stun and pass the Circus Kong. Using Pink Blocks and the Cannon Kong, they can then reach and free the Key Mini Mario, which is blocked inside a cage of Rock. Afterwards, they should head to the locked Goal Door at the bottom right corner of the level, with the Key Mini Mario being brought first.
The M Coin is on a small platform above the Cannon Kong. To reach the coin, the player should draw a long Purple Conveyor to the platform and have the Minis get on it with the help of the Cannon Kong.