StrawberryMilk's any% route is an old one, and a faster route has been discovered. It is as follows:

-Mash text -Get Luigi -Walk down, get Blue Noki (use different swings) -Walk up-left, get Green Noki (throw a charge pitch) -Walk up, get Red Noki on the shell -Exit Mario Stadium and go to Yoshi Park -Get Shy Guy and Blue Shy Guy (ferris wheel) -Exit Yoshi Park and go to Peach Ice Garden -Get Toadette (mushroom puzzle) -Walk up, get Green Toad from the upper-left bush (hit to center) -Exit Peach Ice Garden and go to Bowser Jr's Playroom -Score 1 run in the top of the 1st, then bunt through the rest of the game -Mash text -Enter Bowser Castle -Score 10 runs in the top of the 1st to get mercy rule (though if you are a beginner, you can just score 1 and bunt like with the first game)