To unlock characters, do the following:
Character 23: collect 50 deletes in Time Attack 60
Character 24: collect 150 deletes in Time Attack 180
Character 25: collect 250 deletes in Time Attack 300
Character 38: collect 500 deletes in Time Attack 600
Character 39: complete level 1 in vs. CPU
Character 40: complete level 2 in vs. CPU
Character 41: complete level 3 in vs. CPU
Character 42: complete level 4 in vs. CPU
Character 43: complete level 5 in vs. CPU
Character 44: complete level 6 in vs. CPU
Character 45: complete level 7 in vs. CPU
Character 46: complete level 8 in vs. CPU
Character 47: complete level 9 in vs. CPU
Character 48: complete level 10 in vs. CPU