You have to defeat Arcade Mode. After you defeat Arcade mode with a different
character each time, you will get yet another new and different character. Once
you beat Arcade mode and unlock all characters, There is one left. Venus should
be the last one you unlock from Arcade mode. After you acquire Venus, Beat
Marathon mode to unlock Aphrodite.
Invincible mode:
Successfully complete arcade mode with all nineteen characters.
Top Collector mode:
Successfully complete arcade mode with ten characters. In this mode, you have to
collect as many bras as possible as Venus.