When an user is globally banned, it might be useful to know whether they take part in a mentorship program at any Wikimedia wiki. As of today, there is no simple way to figure that out

GrowthExperiments in its current shape isn't really cross-wiki aware, and there's no reasonable place to put a global list of mentors. I see two possible approaches we might take:

• a Toolforge tool, that'd periodically scrape MediaWiki:GrowthMentors.json from all wikis, and display a list of mentor lists, with a possibility for searching
• fake a "mentor" group via a hook, which would show at existing MW-native tools like Special:CentralAuth

The first solution seems to be better from a technical perspective, as mentorship is really not an user group (at least not now), and showing it in the Groups column might be confusing.