I think TTar and Gourgeist form a sweet combination tbh. They both cover each other's weaknesses well. If the opponent lacks a Bisharp/Mega Gengar, giving TTar a Ghost-typing would only benefit it after a DD boost. As Electrolyte mentioned, Gourgeist can also use Trick or Treat to take away the opponents resistance/neutrality to Tyranitar's boosted STAB Crunch.
Another thing I have been trying out with limited success is pairing Gourgeist with Kangaskhan. Normal/Ghost is a sick typing, giving Kangaskhan an immunity to Normal-, Fighting-, AND Ghost-type moves, and is only weak to Dark-type moves (which can admittedly be annoying). Small Gourgeist has 99 base Speed, so it can actually move faster than Kangaskhan if it goes Jolly and Kangaskhan goes Adamant. Kangaskhan has access to Shadow Claw, so with a Ghost-typing it receives a strong STAB to eliminate Ghost-types (I used it over Fake Out). Gourgeist can then spread Ghost-typing on the opponent's side to make them fall prey to Kangaskhan's STAB Shadow Claw / Sucker Punch :d Gourgeist can support Kangaskhan further with moves like Safeguard, Will-o-Wisp, and/or Disable.
Despite having the same base defense stats as super Gourgeist, investing heavily in Speed + Jolly Nature makes Gourgeist much frailer than I expected, especially on the specially defensive side. The lack of Protect on either Pokemon also makes it harder to coordinate this strategy (I should change that).