Once upon a time Regina was evil but then she changed her ways and even though they saved storybrooke, there was still evil in Regina and snow wasn't prepared to witness the evilness that happened in the enchanted forest like before, what was snow going to do.
After the ceremony of crowing Regina, she hadn't been seen for a while, she was up to something, something bad, something worse than the dark curse. This was pure evil and this time she will succed in defeating the hero's.
Snow always knew that once a villian always a villian but she thought Regina had pit all of that in the past, but clearly not. But what was Regina planning and how bad will it be. Several months after the ceremony and Regina had finally been spotted but she was seen in Rumplestiltskin's castle, where she knew she could get her hands on anything she needs, it was snow who spotted her but she weren't sure what to say or what to do, so she tried to confront her but Regina was obviously prepared for this.
When snow tried to confront her Regina had her banished to the dungeon, but not no already dungeon, this dungeon was filled with burning flames that tortured your skin and there was no way out. Snow needed to find out what Regina was planning but she had no way of doing that so all she could do is wait.
Regina, dresssed in her wickedly evil dress, strolled into the main street of storybrooke waved a wand and all the clouds turned black, like coals and a strong wind picked up.
David had noticed Regina in the street smiling and laughing. "Regina, what are you doing"
"Finally getting my happy ending"
David replied by telling her how she has a family and a proper ending but what she didn't have was revenge. Regina thrived on it and it gave her more passion to ruin there lives once and for all.
With Regina going back to her old ways, and worse, will anyone be able to stop her and make her realise that revenge doesn't give happiness, it gives guilt and a life of regret.