We shouldn't do this
Anakin being Darth Vader is a spoiler and per meta spoilers don't "age away" so we shouldn't be having our tags contain a spoiler.
It also provides quite a nice distinction between the two sides of the person. Anakin and Vader are not really the same person, from a certain point of view, and so it helps distinguish between which part ...
Let’s get rid of it
It doesn’t help with searching. There’s only one question with han-shot-first and not the phrase “Han shot first,” and it’s closed. There is arguably one question with “Han shot first” that lacks the tag and should have it, but that’s not particularly relevant. Anyone can just search for “Han shot first” (or even easier, “shot first”) ...
I definitely agree that the full tag names are a useful addition to the site - we want people typing e.g. the-original-series to be able to find the right tag, and the possibility of synonymisation means that no information would be lost and people typing e.g. TOS would also find the right tag. However ...
How about using the full names as synonyms for the ...
The main tag has been selected as incredibles-2 with the-incredibles-2 as a synonym of it now.
The film is called "Incredibles 2" not "The Incredibles 2" so we should be using the incredibles-2 tag. And for what it's worth I have rolled back your tag edits for this reason.
As for if a synonym is appropriate in this case, I would assume so to avoid cases ...
Rename it and create an 'Avengers' convention
Create a new tag called avengers-age-of-ultron and either make age-of-ultron a synonym (this allows people to find it) or delete it. Additionally, this can create a distinction between the movie and the comics of the same name.
Create a tag called avengers-2012 so that we can make the-avengers-...
I propose a slight variant of your suggestion: that
origins should become a synonym of history-of.
As mentioned in the accepted answer to the previous question you mentioned, origins is a subset of history-of, and there are questions covered by the latter but not the former (e.g. about the development of an idea in SFF rather than its origin).
UPDATE: merge and synonymisation complete.
You missed one: parallel-universe with 54 questions. Since there doesn't seem to be any widely agreed-upon difference in meaning between "parallel universe", "alternate reality", and "alternate world", and they're usually if not always used to mean the same thing:
I propose that all three of these tags should be ...
I can see the point of editing the name to make it a bit clearer ( terminator-franchise perhaps?) but not the point of deleting the entire tag.
There's a world of difference between Terminator (The 1984 film) and Terminator (the entire fictional universe that covers films, a TV series, comics, graphic novels and novels)
No, we don't.
We have 37 questions tagged with any of those tags. Of those 37, we have
26 questions tagged with just mass-effect
1 question tagged with just mass-effect-2
4 questions tagged with just mass-effect-3
The tag wiki excerpt for mass-effect-3 already says that it should always be used in conjunction with mass-effect.
This leads me to the ...
Yes. The two are clearly synonyms of each other, with one of a far higher value than the other.
I'm torn. On a personal level, simply burninating lightsaber-combat seems the more sensible option, but one that will flood the front page with more than a dozen semi-worthless edits. On the other hand, turning it into a synonym leaves the worthless tag intact.
Yes, synonymize them.
There is, as you said, almost zero difference between them - they're just two different words.
inspiration should be the one that goes, as it seems to have a slightly smaller scope than influences.
Making dc-animated-universe the primary tag is clearer for a user unfamiliar with the material and less likely to be confused with dceu.
If a user tries to tag with dcau, after typing dca, the proper tag name will show up either way.
This seems to be a carry-over from Stack Overflow, where numbers are used to differentiate between different versions of software (e.g. foo, foo2 and foo42). Here are a few Meta.se posts describing a similar problem:
Version specific synonyms can only be created by moderators
Version Specific Tag Validation on Tag Synonym Page
Since we also have a ...
starkiller-base is not justified at this time. No action is needed.
Starkiller Base is not a Death Star (is it not named as such)
Users won't expect Starkiller Base to be included in death-star
starkiller-base is not justified at this time by usual tag creation metrics
No, there is no need for a dedicated css meta tag. CSS is for styling a web page... in other words, for the design of Meta.SciFi. There is nothing the tag can be appropriately used for that is not also covered by design, whose description lists:
For questions regarding the design elements of the main and meta sites e.g. CSS issues
The tag ...
As the site's top expert on the Hunger Games, I should probably weigh in on this.
Individual-book tags are more useful in HG than in many other franchises.
In Lord of the Rings, for example, the three books form a unified narrative, and I think  Tolkien didn't even intend the story to be a trilogy. In Harry Potter, the seven books are ...
Yes, let’s get rid of the [legal-proceedings] tag.
The tag wiki description for [laws] reads:
Questions relating to in-universe laws of a work.
That is an equally apt description of legal proceedings (which doesn’t have a tag wiki of its own). It’s hard to see a distinction between the tags; as such, we should move to abolish one of them. Since [legal-...
"the way the tag ends up being used is based on the word used by the author, not on the meaning of the word."
" We frequently have issues with misuse of tags because people use the meaning of the tag's word(s) instead of an author/community usage."
I think this right here sums up the problem. How people use tags, particularly new ...
I've deleted all the grrm instances, so that tag will be destroyed on next auto-cleanup. There's absolutely no need for it.
A tag synonym would make sense if it re-appears. As it was, the tag was created by a single user, and hopefully he'll get the hint and not add them to any more questions.
statistics → site-statistics
Done. There were only a few questions with each of these tags, and both seem to be used identically.
css → design possibly. If these should not be synonyms, then the tag wiki excerpt for design could use some clarification.
I'll let someone else handle this one, since I don't know enough about website design to even know ...