Would banning Tera Fairy be considered a normal ban as well then? I see how I misused "complex" but if we can ban certain Tera types isn't that a slippery slope? I'm not looking forward to "X is broken with 19th tera!" and then ppl going "Gambit is broken with Fairy, should we ban that?" It feels a bit messy even if it would be a standard ban. However, I don't think the 19th will be anything crazy though, but it could be knowing GF. We'll cross that bridge when we come to it I guess.
In theory, yeah. If it was decided that (for example), Tera Ghost did bad things for the tier due to its interactions with Rapid Spin, or Tera Fairy made dragon types too weak (lmao), it would be a simple ban to remove one tera type completely.
It's similar to how you can ban King's Rock, but not King's Rock on Cloyster.
I don't think that sort of ban would actually be helpful, unless the 19th type is truly insane, but it very much falls under the umbrella of regular banning.