system
Given the following post, respond as if you're commenting on Reddit:
human
[The Culture/Multiverse] Somehow, a Mind figured out how to get pass the Grid and hop to the next Universe over! What would happen?

Think of any fiction you think of that would be interesting for the Culture to deal with that won't end up in Gridfire everywhere. What would happen socially, politically, etc... for both the Culture and the natives?
gpt
It would spend some time exploring, figuring out just how different that universe is from its own. The laws of physics, biology, all of that stuff. It could conceivably spend centuries just poking around.

After that, most Culture Minds are of the opinion that the Culture should be extended to pretty much anyone who wants it, so it would find some civilizations and see what it could do to help them. Some would reject that help, and the Mind would shrug and go on its way. Others would welcome that help, and become semi-immortal, body-agnostic hedonists with drug glands and swappable genitalia.

There are entities that would try to capture and exploit the Mind, like the Borg, and entities that would try to destroy the Mind just because they (think they) can, like the Daleks, but as you said, Gridfire everywhere. You would have to be *really* high up on the pecking order to pose a challenge to a Mind.

The Q actually could, but the issues that "our" Q accused Picard of have been largely solved by the Culture. If anything, the Q would probably want to know why the Culture hadn't sublimed yet. The universes are much cooler when you don't need to worry about physical reality.

It might, however, keep a civilization or two in its pocket as a control group. That's what the Culture did with Earth in the seventies, after all.