Earn a T-shirt (or plant a tree) by helping Nim getting better:
https://nim-lang.org/blog/2020/10/01/hacktoberfest-with-nim.html
And tag spammy PRs as invalid
Already doing that in the website repo. (Seems to be most popular with the spammers)
I don't know what's going on this year (I've seen some article complaining about the widespread spam), in previous three years of Hacktoberfest I never noticed such a huge amount of low-effort PRs, and it is still just October 1st.