The set is Gengar @ Gengarite. Nowhere is Shadow Tag in the set. What happens in battle happens in battle. It's a teambuilder ban.Though there is the double standard of stuff like Gengarite Gengar having access to Shadow Tag despite the bans. If that doesn't qualify as a complex exception then I dunno what does.
Edit: Actually, banning Gengarite Gengar as a byproduct of Shadow Tag being banned would actually be complex lol. The current ban is simple.