Get the following unlockables:
Challenge mode: get over 3,000 meters in Endless mode
Time Attack mode: get over 300 points in Score Attack mode
Purple Yoshi: finish Challenge mode with no points
Green Yoshi: score up to 60 points in a Baby Mario level
Blue Yoshi: score between 60 and 80 points in a Baby Mario level
Pink Yoshi: score between 80 and 99 points in a Baby Mario level
Dark Blue Yoshi: score between 100 and 119 points in a Baby Mario level
Yellow Yoshi: score between 120 and 139 points in a Baby Mario level
Red Yoshi: score between 140 and 159 points in a Baby Mario level
Black Yoshi: score over 160 points in a Baby Mario level
Bronze Yoshi: get over 10,000 meters in Endless mode