In tournament mode, beat the normal tournament on all 3 courts.
After completing the first cup in normal tournament doubles, you unlock this ability for Yoshi. Now every time you do your defensive power shot with Yoshi, he will change colors according to egg color he rolls in.
When you get to the main menu, push 'B' to go back to the 'Press start' screen, then hold 'Z' and then press 'Start' or 'A' and then Event games will be unlocked.
To unlock the hardest difficulty level beat the 3 tournaments of the star cup.
Beat all 3 normal tournament cups to unlock this blast from the past.
Beat both Special tournaments, Fire and Thunder, in doubles matches.
To unlock the Star Cup beat the 3 tournaments of the Normal Cup.
Beat normal flower cup in doubles, to unlock Wiggler (Defense.)