Son Goku of the Dragon Ball saga is a god who attains Super Saiyan status. The classic shonen series is very battle-focused, and Goku constantly evolves when faced with new challenges and antagonists. Sailor Moon is a shojo classic that may focus plenty on friendship and romance, but it also has a decent amount of battles in each episode and high stakes.
Sailor Moon and her fellow Sailor Guardians, like Goku, need to evolve to match the strength of their villains. There's a lot on the line for them — to the tune of the universe ending. Between Sailor Moon, her evolved allies and her notorious antagonists, there are a fair few characters who would be a worthy challenge for Goku; some could best him in a skirmish, and some stand a solid chance of beating him entirely.
Queen Metalia Grows Stronger with Human Energy
It would be hard even for a god to go up against an evil space entity like Queen Metalia. Queen Metalia feasts on human energy, and the more human energy she gets, the stronger she is. She has a great system set up where she corrupts people into becoming her generals, and they also control many monsters — youma to assist with the energy harvest.
If Queen Metalia collected enough energy from Earth, she could pose quite a threat to Goku. The only thing Queen Metalia would have to do is corrupt someone, preferably someone close to Goku, and then combine with that person as she did with Queen Beryl. If Queen Metalia were to combine with Vegeta, for instance, it would be lights-out for Goku.
Prince Demande Led the Charge Against Crystal Tokyo
Prince Demande is a formidable war general. Crystal Tokyo represents an elysian future for Neo-Queen Serenity and Prince Endymion. It's a kingdom of hard-won peace, protected and overseen by two of the greatest monarchs the universe has ever created. The dark Prince Demande is such an effective war general that he breached that city.
If Prince Demande were to turn his tactical eye against Son Goku, Goku would need to move quickly to amass his own defense. Prince Demande can even send his own warriors through space and time, which gives him manifold opportunities to manipulate the circumstances of war. Demande also has extreme mental acuity — he can hypnotize even the strongest of foes for certain periods of time, and even ousts the master manipulator Wiseman from his own mind.
Queen Nehelenia Traps People in Her Web
Queen Nehelenia is one of the rare Sailor Moon villains that comes back to haunt Usagi Tsukino and her allies after her initial defeat. Most of the time, after a villain is defeated, trapped or healed, that's the end for them, but Queen Nehelenia is a horse of a different color. Queen Nehelenia wields the Golden Crystal, which amplifies her powers. She even manages to corrupt Tuxedo Mask in Season 6, so it's not difficult to assume she could seduce and corrupt Goku's noble heart.
Not only can Queen Nehelenia control a team of evil people to serve her, which would outnumber Goku, but she can also splinter parts of herself off. Her pale echoes, namely Zirconia, are still scary and have powers of their own. Queen Nehelenia has psychic powers, and she can trap her enemies in her spider webs and inside mirrors. These artifacts would likely trap Goku, at least for some time.
Sailor Chibi Moon Has Untold Potential
Sailor Chibi Moon may not be able to take down a powerful opponent by herself yet, but Sailor Moon sheds some light on the grand future Chibiusa has as the firstborn daughter of Neo-Queen Serenity. Sailor Chibi Moon is destined to follow in her powerful mother's footsteps. The Serenity line is one of the most powerful matrilineal lines in the universe.
Sailor Chibi Moon is about the equivalent of 8 years old, but she's truly 900 years old and could live a close-immortal life traveling through space and time to save the universe. Just like Son Goku, the more Sailor Chibi Moon ages, the stronger she gets, and she evolves into Super Sailor Chibi Moon by the end of the series. If Sailor Moon can do something, it stands to reason that her daughter will eventually be just as powerful.
Wiseman Is a Master Manipulator
Wiseman's persuasive magic is so strong that he turns Sailor Moon's daughter, Sailor Chibi Moon, evil in an afternoon. He also exerts mind control over his general, Prince Demande, who is actually quite a good person. Wiseman's persuasion is so powerful that he hypnotizes Sailor Moon by proxy.
It would be all too easy for Wiseman to slink into Goku's mind and control him. All he needs to know is some of Goku's shortcomings and insecurities. Wiseman conquers moons and planets for fun, with at least one successful major campaign under his belt. Goku would really have to gird his mind to withstand Wiseman's full-effort psychic attack.
Sailor Saturn Has Death Powers
Even a god can die, and Sailor Saturn's powers are some of the most feared and revered because she is the Sailor Guardian of Death, Destruction and Rebirth. She may be of diminutive size, but she also wields the Silence Glaive —aka the Scythe of the Goddess of Death. If Sailor Saturn were to ever turn evil or lose control of her powers, it would be catastrophic.
Luckily, Sailor Saturn is a hero rather than a villain, but that doesn't mean she doesn't have powers that could kill a god, like Goku. Sailor Saturn's strength is why it's so dire when Mistress 9 takes over her body — her powers alone allow her to destroy entire planets with little effort. But it would take more than an evil entity's possession to keep Sailor Saturn at bay.
Pharaoh 90 Is an Eldritch Horror
It takes two of the strongest Sailor Guardians to defeat Pharaoh 90. It's therefore pretty unlikely that Goku could defeat Pharaoh 90 just on his own. Not only did it take both Super Sailor Moon and Sailor Saturn to take down Pharaoh 90, it took everything Sailor Saturn had — every once of her power, magic and life force.
Pharaoh 90 is an eldritch space horror; an amorphous blob that shoots out huge red laser beams capable of destroying armies at a time. Goku would have to find a way to go inside Pharaoh 90, along with another equally strong ally to help him fight. Not only would Pharaoh 90 win a skirmish against Goku, but he would likely take his life as well.
Sailor Galaxia Is the Strongest Sailor Guardian
Sailor Galaxia is a dread-inducing foe. She ruthlessly rips Star Seeds from their carriers and keeps hold of them with her golden wrist cuffs. It's a shock to everyone when she reveals that she was once the legendary Sailor Guardian, rumored to be the most powerful.
Sailor Galaxia is so strong that she valiantly tries to contain and forever imprison evil incarnate, the primordial god Chaos, when she comes across it in deep space. She was close to being strong enough to contain it, but it only just overpowers her, turning her evil. When she's evil, she is completely ruthless and probably capable of besting Goku and Vegeta together in battle.
Chaos Is a Primordial God
Chaos is the entity that made all evil and destruction throughout the universe. It's responsible for wiping out entire solar systems and generations upon generations of people. It is the strongest foe ever in the Sailor Moon series.
There are many kinds of greater and lesser gods, and Chaos is an ancient and elemental god responsible for the harshest and worst parts of the universe. Super Saiyan Goku may be able to put up a fight against Chaos, but it's highly unlikely that he would win if Sailor Galaxia couldn't. Even if Chaos couldn't destroy Goku in his Super Saiyan form, it would no doubt possess Goku and use him as his puppet.
Eternal Sailor Moon Remakes the Universe
Sailor Moon may not be able to defeat a moderately trained Goku in her first transformation, but she only gets stronger with each power-up. Sailor Moon has six total Sailor Guardian power-up transformations (seven in the manga). Even in her most rudimentary form, Sailor Moon defeats great foes because she can tap into a power that comes from her entire matrilineal line — generations of Moon Queens — as Princess Serenity.
By the end of the series, Sailor Moon transforms into Eternal Sailor Moon, a winged moon goddess figure. As Eternal Sailor Moon, she defeats unknown primal evil, revives her fellow Sailor Guardians over and over again and remakes the entire universe. She is effectively immortal with attack, healing and resurrection powers. As Eternal Sailor Moon, she could take on Goku even as a Super Saiyan.
