#5 Emma
No, I'm not going to mention the "dances with Santino" gimmick - I'm going to talk about her return to NXT and subsequent return to the main roster.
When Emma came back to NXT in 2015, she adopted a heel persona that was absolute money. While she didn't really win a whole lot of big matches and she never had her hands on the NXT Women's Championship, she was still dominant, she was still a main event mainstay, she still was a well-developed heel character, and she was still putting on great matches week after week.
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She made her return to the main roster in March of 2016 and didn't really have a chance to show off what she could do before succumbing to a serious back injury just two months later. Then, WWE decided to do a complete 180 with her character and turn her into a model-like character called "Emmalina". Vignettes aired for months before she finally debuted as Emmalina in January of 2017, only to immediately proclaim that she was going back to being Emma. Then they took her off TV for four more months.
...what?
Emma would go on to wrestle for the company for six more months (five, if you don't count the additional month that she was out with a shoulder injury) before being released from her contract last October. It's a shame because they could have done a lot more with her.