when you report someone, who receives the report? Mods on my instance? The mods of the specific community I'm reporting from?

When a report is made, it goes to three instances.

1. The instance of the person making the report
2. The instance of the account being reported
3. The instance of the community in which the content was posted

Each instance only gets a single copy of the report and that report can be actioned by the admin of the instance the report is on, or moderators of the community. Only a single report is generated for each instance even if it meets multiple criteria, and it is one report per instance, not one report per admin/moderator. Marking a report as complete on one instance does not mark it as complete on another instance.

If a report leads to content removal, that removal will only federate if the reported content is removed by a moderator of the community, or by an admin of the instance that hosts the community or the user. If removed by any other admin, the removal doesn't federate to other instances, and is purely removed for local users.