Four player mini games are simply free-for-alls.
A giant angry Blooper has smashed your boat an wants to suck you in with a whirlpool. Avoid him until time runs out, along with debris.
The post office was overfilled with letters and they flew everywhere, so try to get each letter that goes by and give them to Shy Guy by going to him. White letters are worth 1 point, while love letters are worth 3 points. Whoever gets the most wins.
Run away from the moving boulder in the cave so you don't get squashed. Make it out of the cave to win. Don't run into any obstacles. If you get squashed, you lose!
Watch each box being x-rayed to see what is in it. No one loses in this game; everyone plays to get coins to keep. Boxes contain coins and bags of coins. They also contain punching gloves and Bob-ombs, but finding those will daze you.
Find the one card out of the three that is different. First one to two wins. If you pick wrong, a Thwomp will hit you and you won't be able to choose the next round.
Press a different button than everyone else to rise on your platform. If two or more opponents hit the same button, they won't advance. First one to 3 wins.