Velma Green the Spider Queen is the main antagonist in the TV movie Billy & Mandy: Wrath of the Spider Queen.
She was voiced by Kari Wahlgren.
Velma seemed to developed a vengeful, mean, and slightly evil personality based on the fact that she thought Grim cheated when he was chosen to be a reaper. However, she found out that her name had been in the basket he had been dumping into the voting cauldron, due to Grim thinking that she deserved to win the most.
Velma was once Grim's best friend but their strong friendship later dimmed when Velma thought that Grim had cheated to be the Grim Reaper, causing Velma to lose all the love and respect she had for Grim (in reality, Grim had tried to help Velma win). She swore to avenge herself by destroying Grim
However, Mandy showed Velma how wrong she was for falsely accusing him of cheating when a stray paper revealed her name, which Grim revealed that all the votes were for her because she would've made the best reaper in their school. Velma renews her friendship with him when he tells her the truth. Enraged, he unleashed an impressive display of his supernatural powers and terrorized his longtime nemesis for trying to embarrass Velma, which lead to everyone who hadn't already voted to vote for Grim instead.
In the end, Velma tells Grim that she'll probably just rule the world like her dad, Skippy, always wanted her to--early on in the film. However, given that in further episodes the spiders are not controlling the world just like at the end of the film and Velma is nowhere to be seen, it's easily to deduced that Velma may have been defeated offscreen or made amends with Jeff and called off the takeover.
Grim Adventures of Billy & Mandy