Does the word 'God' with a capital G have a plural form?

This is not a problem of monotheistic preference.

When capitalised, the word god is a proper name. So from the pure grammatical point of view, it can have a plural form in the same way as John or Peter (credits to jgelacqua's comments)

It's like Yahweh or Elohim (actually this is a plural I believe - which shows that monotheism in the bible is a fuzzy notion).

"God" is a proper noun. While proper nouns can be pluralized in some cases, it is not very common, and especially not so with "God".

However, I can think of an example. Here is an example with the proper noun, "Bob":

How many Bobs would it take to beat up Charlie?

That is, if Bob could be copied and the copies could fight Charlie, how many would it take to beat up Charlie? This example can be revisited with the proper noun, "God":

How many Gods would it take to beat up Satan?

Sure, why not?

If I don't presuppose that the term refers to one Supreme Being, I can imagine that there are more Supreme Beings. Gods and Goddesses. Unsurprisingly, the word "Gods" does appear in writing. What about the Fates, the Graces, the Norns? Burger Kings or Targets or KwikMarts? What about Egyptians or Armenians, Tudors and Plantagenets, or Kochs or Kardashians?

An interesting construction I discovered on a Hindu information site is "Forms of God" (as well as "Forms of Goddess"). This is an interesting plural, for a presumably (but not necessarily) different God-concept.

I suppose it a philosophical, religious, and/or metaphysical question whether the capitalized "God" is a name, a description, an honorary label, or something else. The different possibilities don't change the fact that mechanically, you can pluralize God. Whether one does so or not will depend on the meaning of the of the name/symbol/label to that person or group.

It might be illustrative to compare it to something more unique than a person's proper name. While we expect there to be many Bobs and Johns, talking about "Gods" may be more like talking about "Englands" or "Swedens". Or "Princes" or "Madonnas"…

Grammatically sound, semantically a little strange, but possible. I suppose you could say things like "Traffic-wise, there aren't many Englands in this world" and "Stricture-wise, there aren't many Gods in religion".

Then again, people use "God" to refer to quite different concepts. I'm sure you could argue that two different persons' Gods (!) are as different as two different Bobs.