Win:
One way to cheat the system, especially in the playoffs, is to save your game, then configure your lineup and sim the results. If you lose, don't save. Reset the game and reconfigure the lineup based on their previous performance against that same pitcher. When you win, save the game again. Repeat to never experience defeat. It's the fastest (cheapest) way to win a World Series.
Big Batter:
To hit a homerun every hit, make a player named Erik Kiss. You can put him at any position and change anything but his name. Put him on your team and he will hit a homerun almost every at bat.
Sucker The Padres:
When playing in the franchise mode, the best way to improve your team is to trade for Oliver Perez of the San Diego Padres. You can trade a much less valuble player to get Perez, and he will be well worth it. Every franchise I've done I've got him for nothin and he's won multiple Cy Young Awards, never having an ERA over 3, plus he's in his early 20's. If you're gonna make any trades make it this one.
Fantasy Draft mode:
Complete a season with an undefeated record.
Retro uniforms:
Win the home run challenge.
