Gender is a scam buy my strawberry cram

It's incredibly out of character for her to blindly trust a stranger who won't reveal their name to her. She mentions several times during the course of the series that she doesn't trust people (especially people she's only just met), but Zhan Tiri wouldn't even tell her who she was, and Cassandra just decided that what this strange ghost child in a weird and dangerous house had to say was more important that a friendship built over the course of a few years, even if that friendship was currently strained.

Her rancor was poorly sourced. There were legitimately several things Cassandra could have been mad about, even directed at Rapunzel. But being mad at Rapunzel for Gothel choosing to kidnap her and abandon Cassandra was an unsympathetic way to go. She sang a whole song about not wanting to be second best anymore, about always waiting for her time to shine. But that entire story beat was thrown out the window in the face of "I am Gothel's biological daughter". She had one (1) glorious line of, "I'm not taking orders from you anymore!" and then all of that was put to rest in favor of, "My mom abandoned me, so I'm going to blame the abuse victim that she kidnapped."

She kept talking about her destiny, but didn't seem to have any goals beyond "be first over Rapunzel." She never even said what it was her "destiny" to do or be. She wanted to take over Corona? And then what? It's not like this was some long-standing desire of hers. Which leads me to

Cassandra spend the majority of her life defining herself as strong-willed, distrustful, and thinking for herself. But they decided that Zhan Tiri could get into her head as easy as that and start full-on manipulating her from the word "go," and that we'd all just handwave it away and accept that Cassandra was doing villainous things because she was being manipulated. Well, nay, I say. Cassandra was an adult with her own mind, and manipulation isn't as instantaneous as that. They didn't even try to portray it like they did with Rapunzel and Sugracha as complete magical mind control. No, it was Cassandra being given choices and choosing the things that would benefit her and/or hurt other people over and over and over again. But we're supposed to be sympathetic towards her.

She assaulted and kidnapped people, attempting to kill Rapunzel or at very least leave her for dead multiple times, then was surprised to find out she was the villain. And honestly, that surprise does a lot to make me dislike her villain arc. I love me a villain who thrives off their villainy, who revels in it, like she did at the beginning of "Cassandra's Revenge." And even villains like that can be redeemed. But people who choose violence and revenge and hate and are then surprised that they're the villain don't impress me.

Her redemption was rushed, crammed into the last twenty minutes of the series - her realization and apology was literally given about a minute of time - and she only realized she was wrong when she lost. Up until the moment Zhan Tiri wrestled the Moonstone away from her, Cassandra was convinced that she was going to win the day. As soon as she was powerless, she was sorry. And then, she was forgiven by everyone because she was forgiven by Rapunzel.

And things that don't go on the list because enough people disagree with them, or because they don't exactly line up with "why we dislike her villain arc" but are still things that bug me, personally:

That Gothel was her mother at all. I hate that plot point. It's stupid, lazy, and makes no sense.