#3 Vampiro
Vampiro's mysterious and frightening look would probably have worked in WWE, and fans would have loved to watch him wrestle the likes of Kane, The Undertaker, and Mankind. He was a WCW mainstay for around three years in the late 90s, until the company went down.
He had spent almost the entirety of his career in Mexico before he made his way to WCW in 1998. His character was similar to WCW legend Sting in a lot of ways, and thus the company paired them up in early 2000.
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Dubbed as "The Brothers of Paint", Sting and Vampiro's alliance didn't last long. He turned on Sting at Spring Stampede 2000, which was followed by a brief feud between the two.
Vampiro has claimed that he was hospitalized while WCW was being purchased by Vince McMahon. He was informed by the WWE creative team that there were no plans for him, and he would not be brought in following the purchase. He went on to wrestle for several other companies, including a brief stint in Impact Wrestling.