Ahh, I remember this game~ I couldn't understand the story but I liked the gameplay~
Let's see, in Xenosaga there are KOS-MOS, Shion and MOMO (They are counted as one unit), various Gnosis enemies~
In Tekken: Jin, Heihachi (Enemy, then ally), Devil Jin (HARD enemy), and King and Felicia.
In the Tales series, they only took character from Tales of Destiny series, so there's Stahn and Rutee, and Leon/Judas, and various enemies (Green Ropper is one of the most annoying enemies in the game. They can poison you~)
In Megaman, they only used characters from Megaman Legends series, so you have Megaman and Roll, Tron and Kobun, Juno (enemy), and various reaverbots~
There are LOTS of characters here (Ryu, Ken, Karin and Sakura, Klonoa and Gantz, Bravoman and Wonder Momo, Morrigan & Lilith, Rose, etc....), but unfortunately, you only get to pick 10 of your favorite characters for the final battle (which lasted 2 hours for me). Oh, and you can't go back to previous maps to level up. There are a total of 50 stages in this game, each lasting at least 1 hour each (except the introductory battles).
For those who wants to play this, here's a tip for you. Don't think you've almost won a map when there's one enemy left. Enemies WILL ALWAYS have reinforcements (So annoying really)~