I actually played a each mode online. The first one was a race on Music Park. Everyone had faster karts I think, but nobody knew how to drive. I swear I witnessed at least 10 instances of someone going past me but falling off the course. I ended up in third because everyone but me had a star at the end.
The second was a balloon battle on Sherbet Rink, or whatever the name is. I had no idea that there weren't teams like in the Wii game until the end of the battle. I kept trying to find someone with the same colored balloons as me, but I was having no luck. I somehow managed to win despite my most powerful item being a super leaf.
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