Name: King Ghidorah
Why he should be end game boss:
Goku and Vegeta, Coke a cola and Pepsi, Mario and Bowser, Link and Gannon, Batman and Joker.
Everyone has their arch nemesis. Godzilla's arch-nemesis goes by many names. King of Terror, Destroyer of Worlds, Space Demon, Planet Killer, etc. King Ghidorah's origin differs on which continuity the film takes place but his first and most popular origin is that of a space monster who goes from planet to planet killing off all life, including advance alien civlations like the one on Venus, turning the entire planet into a waste land killing off a race more advance then us.
For fun.
In a weird way he is indirectly responsible for Godzilla and other monsters coming into existence. By wiping out the dinosaurs and many other life forms during the K-T extinction event he has allowed the rise of man who in their arrogance ended up accidentally creating new monsters including mutating leftover dinosaurs King Ghidorah failed to kill.
King Ghidorah is in many ways a worse monster then Godzilla or most earth monsters. Godzilla or Rodan may destroy entire cites, King Ghidorah will destroy the entire planet if not stopped. King Ghidorah's earlier film appearances had him spazzing out like crazy shooting entire volly's of Gravity Beams from his three mouths, spamming them like crazy while moving his heads in random diractions, often destroying or hitting random targets.
King Ghidorah is unpredictable, making it impossible to dodge all of his GB spamming as half the time he seems to miss on purpose only to rake the enemy with 30+ beams in only a few seconds. He's also very durable, in the older films often requiring both Godzilla and Rodan (Godzilla's equal in the old days) to kick his ass and make him leave the planet. It wasn't until the film Destroy All Monsters where 3 monsters killed him once and for all (original continuity wise).
Also story mode could work in Mecha-King Ghidorah )second picture) very easily, like after he is beaten aliens or humans take his reamins and turn him into a cybornatic weapon, Mecha-King Ghidorah. Could be a bonus boss as an Epilog Chapter.
King Ghidorah is timeless as he has menaced Godzilla in all three film series.
Name: MechaGodzilla
Why he should be a boss:
Mechagodzilla is pretty well known and is arguably Godzilla's other arch-nemesis. Whenever Mechagodzilla fights Godzilla he almost always brings him near death. His origin and weapons change depending on the continuity. In the 1070's films he was built by aliens who wanted to conquer the world. He had shit like finger missiles and rainbow color eye lasers. In the 1993 film he was built by the U.N. to kill Godzilla and had stuff like Shock Anchors it can fire from it's wrists to zap the enemy from the inside out, his armor absorbed energy attacks like Godzilla's breath to power his stomach cannon and he had an aircraft called Garuda that would attach to it's back allowing more mobility during flight and more weapons.
The 2002 version was a cyborg built around the remains of the first Godzilla and armed with an Absolute Zero Cannon that freezes the enemy solid.
One thing stays the same, no matter the incarnation Mechagodzilla always has an all-out assault attack and a powerful cannon of some kind built into it's chest/stomach.
Much like King Ghidorah, Mechagodzilla is a timeless villain as he has menaced Godzilla in all three film series.
Name: Hedorah, The Smog Monster
Why he should be a boss:
King Gidorah was the most dangerous and unpredictable monster back in the original series.
Mechagodzilla was the strongest monster back in the original series.
Hedorah was the toughest in the original series. Practically immune to physical harm unless hitting something vital like his eyes and hardly harmed by Godzilla's atomic breath, Hedorah is the hardest monster kill because he is hard to harm. He feeds off of toxic waste, allowing him to fly by shooting out sulfuric acid from his flying form which chokes other monsters and melts people. He can shoot a laser from his eyes that cause a stinting burning effect even when the beam ceases as if hit with acid. Speaking of acid, his blood is acidic and if he ate enough toxins it can either cause mild burns on a monster or reduce a monsters hand to a shivered prune, almost leaving nothing but bone. He can even fling bits of himself at other monsters to burn them.
Truth be told Hedorah could easily make a final boss plus he never was a boss in a game, at the very least he could make a sub-boss like Goro since he is so durable.
Name: Biollante
Why she should be a boss:
JUST. LOOK. AT. HER.
If that doesn't scream boss material then nothing does. Biollante was introduced in 1989 and is a weird monster as she was made from combining the cells of a rose, an Asian women and Godzilla himself. The result is a nightmare of teeth and mouths. This part plant/human/animal hybrid can spit energized acid that zaps Godzilla and then burns away at his skin when the energy disapets. Her spear shaped vines punch through Godzilla's hand and shoulder like they were nothing which is amazing as only one other thing has been able to break through his bones. Her extra mouths of course wrap around the enemy and either bite or spite acid. Her huge mouth is lined with rolls of teeth all over and cause a lot of damage when she bites down.
Overall she's pretty tough and her battle with Godzilla ended with her winning. Proof that monsters worse then Godzilla can be made from his own DNA. Her Rose form could make for a cool early boss and her final form could be a bonus/secret boss that you fight after the end credits are done rolling. Basically Godzilla or whoever you played is swimming or flying back to Monster Island after beating the final boss, credits roll and if the right conditions you get a bonus chapter called Epilog: Fallout where your monster makes landfall on Monster Island only for her spores to fall from the sky and Biollante rises up for revenge this time as her Final Form.
Name: SpaceGodzilla
Why he should be a boss: Showing up in easily one of the worst Godzilla films ever, 1994's Godzilla vs Spacegodzilla, Spacegodzilla's origins are unknown. Somehow Godzilla cells ended up in space and mutated into this sick twisted monster. Theory is either being spores from Biollante going into space or Godzilla skin stuck on Mothra and falling off when she flew out to stop an asteroid from hitting Earth after her battle with Godzilla.
Whatever the case he has....some pretty fucking awesome powers that would be rad if NRS can do pull it off masterfully.
http://tohokingdom.com/articles/analysis_spacegodzilla.htm
If used a lot of care must go into the glowing and pulsing effects for him and his Crystal Fortress.
Why he should not be the final boss:
He was already the final boss of two out of three of Pipeworks/Atari's Godzilla games. He can make for a cool boss, maybe as a side plot bonus boss but not the final boss.
Name: Destoroyah
Why he should be a boss:
In 1995, Toho introduced one of the greatest villains in the Godzilla series.
Godzilla was mutated from atomic bombs. Destoroyah was born from the only weapon ever to kill the original Godzilla; The Oxygen Destroyer. Once a colony of microbes, Destoroyah soon mutated into this thing. At the time of their battle Godzilla was suffering a massive power overload mutating it into the planet destroying Burning Godzilla. Destoroyah is tough as it was able to fight the super powered Godzilla evenly and take several of his now roid up, stronger atomic breaths with no trouble up till Godzilla was near meltdown.
Also he killed Godzilla's son.
Animation note: If used he MUST have chemical smoke coming from him as he did this a lot in the film.
Name: Monster X
Why he should be a boss:
Godzilla's latest villain from 2004, Godzilla: Final Wars.
He was never in a game yet.....and he has a secret....
Name: Burning Godzilla
Why he should be end boss (if playing an evil monster):
Screw fighting normal Godzilla, let's have a real challenge.
In 1995, Toho killed Godzilla.
To do this they did something ironic. Godzilla feeds off of radiation but what if he absorbed too much of it? He became a super monster, his skin burning, glowing and pulsing in places as steam raised from his body. His normally trademark blue Atomic Blast had been replaced by a now red-orange one with a lightning bolt spiraling around it. Godzilla had now become more powerful then ever.
Too powerful.
When his body 1200 degrees Celsius his body would meltdown while the energy would continue to rise in temperature until the atmosphere would ignite and the whole planet and everything on it would burn up and die with him.
Even Destoroyah, a monster born from the chemicals of the only known weapon to kill the first Godzilla, a creature who would have easily killed Godzilla if he was normal could not stop the now overpowered Godzilla.
Special animation note: He MUST have smoke and glowing-pulsing rashes as he did this constantly on film.