Ensemble Dark Horse: Every monster in the game has its fanbase, but Biollante is probably the prime example after being axed from appearing in Save The Earth.
The Final Wars redesign of Gigan in Unleashed is definitely this.
Game Breaker: Destroyah's Horn Katana in Unleashed can chop health bars to bits, especially the overhead swing.
What makes it OP is that, unlike in the previous games, it costs no energy, so he can just spam it like Hell.
Obvious Beta: While the game itself is complete, there were several elements in Unleashed that were unpolished, such as Godzilla 1954, and many of the features promised in the developer's diary went unimplemented due to lack of time and money.
Rescued from the Scrappy Heap: While not received very well in the similarly ill-received Godzilla vs. Megalon, Jet Jaguar has since found redemption in the eyes of fans through Save the Earth and Unleashed where he is a very fun character to play as and has fared better overall.