Okay, take two:
STARTING ROSTER:
1) Leonardo
2) Donatello
3) Raphael
4) Michaelangelo
5) Splinter
6) April
7) Casey Jones
Shredder
9) Baxter
10) Rat King
11) Leatherhead
12) Karai
Unlockable:
13) Krang (beat Arcade mode)
14) Mona Lisa (beat the hero story)
15) Hun (beat the dark story)
16) Bebop (beat adventure mode)
17) Rocksteady (beat adventure mode)
1
Venus (beat 10 opponents on survival)
19) Mondo Gecko (beat 20 opponents on survival)
20) Agent Bishop (beat 25 opponents on survival)
21) Irma (beat 1/4th of the event mode)
22) Tokka (beat 2/4 of the event mode)
23) Slash (beat 3/4 of the event mode)
24) Fugitoid (beat event mode)
25) Rahzar (beat 50 opponents in survival)
26) Ninjara (beat 75 opponents in survival)
27) Metalhead (beat 100 opponents in survival)
2
Wingnut (beat arcade as 10 characters)
29) Hamato Yoshi (beat the Last Story)
30) Dogpound (beat the dark boss rush)
31) Fishface (beat the hero boss rush)
32) Groundchuck (beat arcade as 20 characters)
33) Dirtbag (beat arcade as 30 charcters)
34) Renet (beat the last boss rush)
35) Carter (beat aracde on hardest)
36) Mutagen Man (beat arcade twice)
37) Armaggon (beat the target test with 10 characters)
DLC:
Mitsu
Muckman
Dragonlord
Drako
Quarry
Non-playable boss:
Lord Dregg