@Xuncu  
Don’t forget Grand King Ghidorah which basically had him as the Kaiju equivalent of Galactus.

@Mechanized Pony
 
@Xuncu
 
Author here. Just to clear up any confusion, the incarnation of Ghidorah used in the story is more or less the version seen in Rebirth of Mothra 3. Ghidorah is a natural creation and does evil on his own accord.

@Xuncu  
Really? Because, judging from what Rebirth of Mothra 3 showed me, King Ghidorah is practically evil incarnate.

@Xuncu  
Yeah, he probably did fly there on his own.

@Mechanized Pony  
Of that, it’s ambiguous. It seems the Xillians do have the tech to do so, but when Godzilla and Rodan fought Ghidora on Planet X,  
I recall that they invited human witnesses. So, it’d be too suspicious for them to transport Ghidora in, so he must have flown in under his own power.

@Xuncu  
Ghidorah’s first film did show him fly off, but it didn’t show him in space. However, he obviously have had to have flown through space to make it to Planet X unless the Xillians gave him a ride there.

DOCTOROCTOGONAPUS!

@Mechanized Pony  
Well, definitely for his first iteration– I don’t remember the movie 100%, but I think there was a scene in his first movie that showed Ghidora flying through space. But making a bioweapon for interplanetary warfare, and not making it capable of traveling under it’s own power would be a huge oversight.

@Xuncu  
I knew all of that minus his Garogan origins because I haven’t seen anything from Zone Fighter, but I do know its events with Godzilla, Ghidorah and Gigan were canon to the Showa Godzilla series. But what I meant was that just as you acknowledged that spores shouldn’t be able to make it into space on their own, neither should anything that flies with just wings. Had Ghidorah traveled through space in a meteor like how he got to earth, then I would accept that.

@Mechanized Pony  
Ghidora has his own wings.  
Plus, he was designed as a bioweapon. Well, at least his first two origin stories:
 
Origional: He’s specifically an inter-planetary terror weapon. Made by the Garogans (their series was Zone Fighter - one of those Ultraman/Power Rangers-style shows), sold to the Xillians , who sent him to earth to ‘soften us up’ so they could conquer Earth themselves. They didn’t know about Godzilla, Mothra, and Rodan (who kick Ghidora’s ass). Then in the next movie, the Xillians show up themselves, and con the JSDF into letting them ‘borrow’ Godzilla and Rodan, as they got Earth to believe that Ghidora was actually attacking them, too. They mind-control the two Earth monsters, get cocky, the JSDF figures a way to break the control, and beat up Ghidora again.
 
2nd: This time Ghidora’s made by a terrorist group of humans from Earth’s future, where Japan becomes a world superpower, due to the government essentially being run/replaced by a conglomerate of corrupt mega-corporations. They go back in time with creatures called Dorats which are bio-engineered super-“pets”. After a complicated plan involving going back to 1944 and trying to replace the Godzillasaurus that would become Godzilla (but it seems he’s a fixed point in time, so when they moved him, he was already mutating, and they put him in the path of a Russian sub, so he ended up becoming even bigger and stronger), the Laos nuclear bomb fused the Dorats into this iteration of King Ghidora.
 
His other origin stories:  
He came in like a wrecking ball…. 65 million years ago. At least he rode shotgun on that meteor.  
The one where he was a good guy: He’s an immature version of Orochi (also strangely a good guy this time).  
Final Wars: He was made by that version of the Xillians themselves.

@Xuncu  
Alright, I can see Mothra’s divineness allowing her to travel through space, but saying Ghidorah could do so because he’s an alien is like saying a xenomorph with wings can too. Also, to Ghidorah we’re the aliens.

@Mechanized Pony  
Mothra is a god, and Ghidora is usually an alien (plus the mecha variation).  
Biollante was a (failed) human attempt at resurrection, not a space program.

@Xuncu  
If Mothra and King Ghidorah could travel through space by just flapping their wings, then I’m sure some sentient monster-plant spores could do the same.

@Xuncu  
black holes have been considered temporal rifts, so in Japanese logic, that’s the best excuse for it.

@Mechanized Pony  
Against gravity, into the vacuum of space, to the nearest black hole, in just a few years?

@Xuncu  
Biollante’s spores drifted into space on their own. Also, I don’t think she died, it seemed more like she just what she did the last time she faced Godzilla.

@Mechanized Pony  
Yeah, died in the same movie. So, how’d Biollante get to space?  
By Mothravator.

@Xuncu  
Yeah, the plant/Godzilla/human-girl hybrid of the 89 film “Godzilla vs Biollante”.

@Mechanized Pony  
You do know who Biollante is, don’t you?

@Xuncu  
It doesn’t really specify that Mothra carried Biollante cells with(especially since they’ve never been in physical contact with one another), the page says that Mothra and Biollante both entered space and both brought G-cells with them.
 
On an unrelated note, has anyone else realized that Spacegodzilla is biologically more of Godzilla’s son than Godzilla Jr.?

@Blissey1  
It’s JAPAN: No hole is unpenetrable!

@Xuncu  
>grew inside a black hole
 
wut

@Background Pony #0544  
Oh, no they have sepcified: it was Mothra that accidentally carried some of Biollante’s human/rose/g-cell hybrid tissue remains into space, which then fell and grew inside a black hole.  
http://www.tohokingdom.com/kaiju/spacegodzilla.htm

@thps48  
Xenilla’s origins never got fully explained. We know some of Godzilla’s cells fused with crystalline bodies under the force of a nearby nova. Not sure how the cells got into space though. Either
 
A. Some of Godzilla’s cells were stuck to the claws of a monster he fought when said monster flew off into space
 
B. A monster that was part animal (in this case Godzilla, not human like previous poster) and part plant floated up into the upper atmosphere as spores after her fight with Godzilla. Some of her cells containing the animal side floated out of atmosphere and into the void.

@thps48  
Ghidora was a good guy in one movie.
 
 
So, yes.