When Anton Mercer is on the verge of a scientific breakthrough, he accidently transforms himself into Mesogog. Mesogog wants to bring the planet back to the glorious era of the dinosaurs, and he will do anything to achieve his goal, and will not let anyone stand in his way. Not even his alter ego, Anton Mercer is able to stop him. Mesogog is finally able to discard himself of Mercer by seperating the new. Once Mesogog gets his hands on the Dino Gems, he absorbs some of their power allowing him to evolve. He is destroyed when the Rangers combine their Dino Powers to stop him.

Zeltrax is a cyborg created by Mesogog, and had vowed alliegence to him. He was formerly known as Terrance Smith, but when he got turned down for a job given to Tommy, he becomes determined to win Anton Mercer's approval. In his anticipation, he is badly injured during an experiement, when there's an explosion. Mesogog finds and rebuilds him as Zeltrax.
After pledging an alliance to his master, he Zeltrax was destroyed by Dr. Oliver. Fortunately for him, he was able to survive with the help of the Tree of Life, which gave him the ability to transform into an advanced form. Since Zeltrax refuses to stop his efforts for ultimate revenge, the Power Rangers are forced to destroy him.

Elsa is a determined cyborg, who is loyal and will do anything to please her master. Little is known about her history, but she seems to hold a secret crush on the Black Ranger.
Principal Randall
As Principal Randall, she is the principal of Reefside High School. She believes making the high school experience as miserable as possible. Principal Randall is a little suspicious of why Dr. Oliver is working as a science teacher at Reefside. She enjoys prowling the grounds and looking for students to send to detention. Meanwhile, she tries to use her secret identity to complete her true mission for Mesogog.
Shortly after Elsa fails her mission as Randall and her identity is discovered, Mesogog drains the powers he gave her, which returns her to the woman she once was. Elsa volunteers to tell the Rangers everything she knows, but Zeltrax kidnaps her and holds her for ransom. After the Power Rangers come to her rescue, she goes back to being the principal of Reefside High and is revealed to have been a close personal friend of Anton Mercer.
Evil White Ranger
When the evil energy that makes Trent evil is destroyed, Zeltrax creates the Evil White Ranger clone, a souless warrior with no trace of Trent. The Evil White Ranger fights alongside the others in Mesogog's army. The Evil White Ranger is finally destroyed in a one on one battle between himself and the real White Ranger.
A mixture of dinosaur dna and technology, the Tyrannodrones were created as an experiment by Tommy and Anton, but are now used as Mesogog's grunt army.
When the Triptoids get sucked out of a video game, Zeltrax recruits them for Mesogog's army.
When Lothor escapes from the Abyss of Evil, he uses his own Power Discs to put Shane, Tori, and Dustin under his spell. Unfortunately his plan fails, and he forms an alliance with Mesogog in order to defeat the Ninja Storm and Dino Thunder Rangers. When Lothor fails to deliver on destroying the Power Rangers, Mesogog finally takes him down for good. Mesogog imprisons him in a jar with his mental powers.
Zurgane guards the Samurai Amulet in the Abyss of Evil until Cam, Hunter, and Blake get a hold of it. He leads the troops out to the Abyss of Evil for Mesogog and Lothor. Mesogog comments on what a good general he is. Zurgane is destroyed again by the Thunder Rangers and the Black Ranger.

Lothor's Bodyguards
When Lothor returns from the Abyss of Evil, he brings with him these two warriors. They don't speak much, but they fight like the dickens. It seems like these two warriors were famous in Japan at one time, considering they have characters based upon them in the Japanese TV show based on the adventures of the Power Rangers. The two warriors help Lothor attack the Wind Ninja Academy and capture the Ninja students. They are also called upon again to fight at the Abyss of Evil with the remainder of Mesogog and Lothor's forces; against the Ninja Rangers and Dino Rangers. They are finally defeated by both the Red Wind Ranger and Triassic Ranger's Battlizers.