Mastodon now has support for importing server-level blocklists. This allows admins to import ready-made blocklists instead of having to block hundreds of instances manually.
If you want a source of blocklists, you might want to try here:
➡️ https://writer.oliphant.social/oliphant/the-oliphant-social-blocklist
There are many lists on that site, with different criteria as noted for each list. There's a very basic list for people who want to keep blocking to a minimum, and a range of longer lists too.