When you are selecting one of the wrestlers from Virtua Fighter, hold the R button before you select your character with button A.

After getting Grace, complete the tournament mode and wait for all the credits are over, then there will be a next match, you will face one of the hidden wrestlers. Defeat that wrestler to unlock them as a playable character.

After getting Tiger, use Tiger to complete the tournament mode and get a total of 200,000 points before you can face Diablo after all the credits are over. Defeat Diablo to unlock him as a playable character.