Vrogs are large, strong monsters which can turn invisible.
Apparently, Vrogs were previously believed by the Troop to have gone extinct in 800AD.
After a Vrog called Todd was dumped by his girlfriend, Cecillia, he refused to let her go and followed her to the Human World. There, when he spots Jake with the necklace he gave Cecillia, Todd immediately suspects that Jake is Cecillia's new boyfriend, and begins stalking and attacking Jake, and warning him to stay away from Cecillia. While Todd is beating Jake up outside the school, Jake lets slip that Cecillia is with Etienne. Realizing that Etienne is Cecillia's new boyfriend and not Jake, Todd immediately abandons Jake to go after Etienne.
That night, Todd attacks the Valentine's Day school dance. Jake, Hayley and Etienne use an accelerator to speed themselves up to Todd and Cecillia's speed, and they confront Todd. Cecillia then pushes herself and Todd back into their home dimension.
Vrogs are very jealous monsters, and once a Vrog becomes fixated on something, it never lets it go.
A Vrog has a roughly dinosaur-like body, with orange, scaly skin, stripes, greenish eyes, a large head, a long tail, and three sets of small, centipede-like arms behind the head.
Vrogs are perfect chameleons, capable of turning invisible. They are also super fast, and they have superhuman strength.