Vampronica is the alter-ego of Veronica Lodge in two of the Archie's Weird Mysteries episodes "I Was a Teenage Vampire" and "Halloween of Horror".
Nilnewz was let into her house before Archie showed up and bit her neck turning her into a vampire and a slave to his master, Medlock. She then wanted to bite Archie, Betty, Reggie and Jughead (though she changed her mind). Vampronica then was introduced to Medlock who was now attracted to her getting on Scarlet Helsing's nerves. Archie and others had to destroy Nilnewz before an hour or else Veronica will be a vampire forever. After a garlic breath Veronica was returned to normal and with her sunstone made Medlock weak.
Vampronica later appeared in the final vampire episode Halloween of Horror as she and her friends had to battle Medlock and her friends who he turned them into vampires. Veronica was surrounded by them and soon was back to Vampronica and took off her sunstone (now a useless trinket). Scarlet was later revealed to be the chosen one and destroyed Medlock which turned Veronica and her friends back to normal.
Vampironica is also the name of an alternate reality version of Veronica, who is also a vampire. The main difference is that this Veronica is a natural born Vampire, as both her parents are later revealed to be vamps as oppose to being turned into one.