How do I beat computers easily in challenge mode?

You can just buy a Power Swing. Buy a special homer power-up for all the batters if you can afford it, and all your batters will hit twice as hard!

Do not follow that guy's lessons, always practice fielding and until you perfect catching balls with lucky glove before every game your good, I played special cup and beat it with much ease with Yoshi's team, and Superstarred the whole team. Preferrably if I were you try to tap A on right timing with bating mode on easy in control and options. Put birdo at short stop and Yoshi on second base with baby luigi as pitcher and baby mario in right field as shy guys are in the rest. If you are good with fielding and catching 95% of the hardest to catch balls go and get a Song note that makes teammates get along it makes all shy guys get along and helps later on, remember never hold A for more than 7 seconds or like 2 seconds before the pitcher throws the ball do it as last second and practice hitting it perfect and remember no holding A with Yoshi baby mario luigi and only hit a homerun with red shyguy and or birdo. Remember do not pressure yourself into stealing bases. Practice it only on first base to second.