Hey Bex! What gimmick do you think Gothel would have had if she had been a spirit? Like Tromus and Sugracha, what do you picture her “Boss Battle” being?
This is such an interesting question, Roy! I read this ask last night and decided to go to bed and think on it because I wanted to give you a really good answer.
So first, I want to go over a few facts that we know. The first is that we don't know what Tromus and Sugracha were like when they were alive. We do know that the "Mrs. Sugarby" guise that Sugracha took on was not her natural one, but "the vessel [she] chose to suit [her] purpose." It's safe to assume that Tromus is the same. Yes, the silhouettes they used in "Lost and Found" were of them, but that was so the audience would recognize them.
Second, let's break down their known powers that seem special:
Sugracha: Can travel unseen through crowds in her spirit form. Can control multiple people's minds at a time (perhaps only if she's giving them all the same task?), using a trigger sound to "activate" them. It's possible that she has a connection to art (I've RP'd a story with her where she could bring paintings to life for combat purposes) but we have no solid evidence of this. The manipulation/mind control seems to be her biggest "trick," though it's a pretty powerful one.
Tromus: Seems to like to collect magical artifacts (we don't know that he created any of the things in his house, only that he had them). Can put/keep people asleep and invade and control their dreams. Built the House of Yesterday's Tomorrow out of sand?
Like Sugarcha, his biggest "trick" seems to be tied into manipulation, something we know Gothel was skilled at as a human.
So I think Gothel's manipulation would continue to be mundane and not magical in nature. I wrote an au RP once where Rapunzel's power didn't come directly from the sun, but was tied to light itself. In that RP, Gothel had power over darkness and shadows. She could manipulate them, travel through them, remove the light from a room by increasing the shadow. In the movie, she used darkness to manipulate Rapunzel a lot, snuffing out her candles, using shadows to create monstrous forms to frighten her, and making sure that she was the only thing Rapunzel could see in a gauntlet of shadowed horrors. She even used the dark of night in the forest by the campsite to make herself more threatening and intimidating, and to seem to vanish. So, I think Gothel's spirit power would be darkness/shadows. It would feed into her drama, as well as her manipulation.
Can you imagine Rapunzel and Eugene and Lance having to fight spirit Gothel in the dark? Rapunzel's C-PTSD triggered not only by her presence, but by all the tricks she was playing that had been used against Rapunzel her whole life? Can you imagine how worried Eugene would be, paranoid that at any moment, there'd be a knife in his side, and trying to keep it together for Rapunzel's sake? Can you imagine Lance just having none of it, and succumbing to a panic attack, because he's skittish at the best of times, but this time he knows there's a threat out there in the dark? It would be horrifying and wonderful to watch.