Mary Ann Rogers is the main antagonist of the 1998 film 3 Ninjas: High Noon at Mega Mountain. She goes by the name "Medusa".
She was portrayed by Loni Anderson.
During the following day, Medusa, her right-hand man Lothar Zogg, her Jamaican sidekick C.J., her three idiotic nephews Carl, Buelow, and Zed, and a small group of mercenaries and ninjas sneaks in and infiltrate the park with disguises. While inside the park, Medusa and Lothar finds the poster that advertises about Dave Dragon and the star force 5 making the performance. Knowing to be viable threats to plans, Medusa orders Lothar and his few mercenaries to capture Dave while she and the other mercenaries were going to the park's control center operations. Medusa's mercenaries begins to commandeering and shutting many places and rides down, impersonating the park ride operators, kidnapping several guests and holding them hostage, including knocking the security guards out to prevent anyone in case who attempts to investigate or actually did get any suspicious about it. Medusa and her men arrive at the park's control command center operations, tricking the security guards into letting them in by pointing her gun at the guard and taken him hostage as ehe and her men took over the park's control command center operations and used it as their base of operations, removing the park's operators and disabling the all technologies and phone connections. She also watches C.J. hacks into the park's central computer mainframe control systems and control all the park's surveillance cameras and closed-circuit television monitors.
Medusa had C.J. dial the park owner, Harry Jacobson, with the video-telephone from his mansion, using the security guard as and she demands Jacobson to pay her $10 dollars ransom and threatens to cause accidents on the rides. After fending Klaus and the thugs that attempts to capture Dave at the backstage after his performance and waking him up to inform about the park being compromised with great deal with several guards unconscious and phone disconnections, he thanks the kids and goes off on his own. Amanda founds the radio that was left behind after their chase and switch the transmit to channel 9 news on the tower and knowledge about them and request Tum Tum to call out a fire to them, which causes the fire rescues and police to be called in the park. However, C.J. and one of Medusa's mercenary spots the police and alerts her about it, where she orders them to open fire, leading to a big shootouts. This causes the FBI led by the boys' father Sam to be called in and arrive to the scene. Chief Young informs Sam about the park's attack until they intercept her call on the FBI van monitors. After Rocky and Sam's communications, Medusa tells the Sam, Young and Andrew about her plans to make Jacobson paying her some large amount of money. Sam request about bringing Jacobson to the park, analyzing Medusa and Park engineer about the ride conditions. Since the Police and FBI are called, Medusa orders C.J. to interface the Avalanche ride and proceed to increases it speed level, nearly putting the lives at risk. The boys are concern for the riders at their risk, but Amanda gives them some of her arsenal weapons and utilizes them for the fight. After the boys fought some of Medusa's mercenaries with Amanda manages to shut off the ride's power control with her laptop and saving the guests, Medusa angrily demands C.J. interconnect the the monitors on kids where they teases her before C.J. capture their face on the camera and prints. Knowing they will interfere with her plans, Medusa summoned Lothar to have her nephews to capture the kids.
Dave tries to infiltrate Medusa's operations after following Lothar to the park's control command center operations and sucker punching Medusa's guard on the face when he tricks him into opening the door under the bunny disguise, he peaks at Medusa and her mercenaries watching the news broadcast that her plans are working as Jacobson should pay where she discovered and orders her men to seize him. Even though that Dave fights them, Medusa trips him down after she uses her own whip and have her men captured and tied him up on the chair before C.J. asks him for his sister's autograph, much to her annoyance. After Colt, Rocky and Tum Tum evades and take her nephews down with carnival's games and their ninjitsu skills, Medusa witness her nephews on the ride screaming in panic on the monitor screen and calls for Lothar, who plans to take out the problems. Meanwhile, Amanda utilizes her laptop to gain access on the park's mainframe central computer systems to lock all of the rides out. While the SWAT team arrives to the rescue the park and stop Medusa, she has her men to rigged the fence with electricity to shock them from entering the park. When C.J. proceed with her plans to hack into the ride systems, he wrestles the controls as Amanda manually locked down some of the ride access. However, Medusa intervenes and quickly has her access locked out on the Zinger Turbo Loop roller coaster and suspends a roller coaster train full of passengers at the top of a loop, Dave tries to attack before she counters him and having her mercenaries to lock him up at the Twister II roller coaster middle loop which is full of hostage of guest. Knowing Dave won't be a problem, Medusa threatens Harry with Zinger Turbo Loop roller coaster full of passengers to their deaths if he does not pay her a large sum of money. With no choice, Sam tells Jacobson to pay the money, to which he reluctantly agree and leave to the commercial bank. While Medusa's mercenaries scares off some of the park's guests for the Zinger Turbo Loop, few of the mercenaries tortures Dave at the Twister II roller coaster middle loop afterwards.
In the meantime, Medusa berates her nephews for making the boys escape and threatens them if they'd failed once more again, but Carl finds the picture footage at the Twister II photo booth with Rocky and Jennifer riding on it earlier and gets one to find her. Eventually, Medusa's nephews found Jennifer and captured her as Carl starts lying about Rocky. Medusa manages to have her nephews kidnaps Jennifer and tying her to the bottom of the Zinger Turbo Loop roller coaster's track and use her as a bait to keep the kids from interfering by threatening to release the train, causing it to run over her if they don't cooperate. But, Rocky goes off on his own to rescue Jennifer. Watching Medusa's nephews tying Jennifer up on the bottom of the roller coaster track on the surveillance footage, she sent Lothar to stop the kids. Rocky arrives and battles with Lothar with sword while attempting to rescue her. After the fight at the top of the Zinger roller coaster loop, Rocky knocks Lothar off with the yo-yo around his ankle and causes him to literally bounce out of the park and into the hands of the authorities stationed outside of the park. Exasperated, Medusa watches the monitor until C.J. alerts her about Jacobson arriving in his helicopter and she orders her mens to gather all their belongings before she releases the brake train. Rocky frees Jennifer and saving her from the passing train. After Harry arrived to the Mega Mountain with Medusa and her men heading over at the fountain, he then begins to give Medusa the $10 million ransom bag by bag as they pick them up on process. But as the final one drops, Amanda managed to use her helicopter to cut it open, destroying it as all of the money rains down and the park guests started to snatches it all. Medusa quickly discovers this, captures her and escapes with her men before Sam and the police raids into the park.
Rocky meets up with his brothers, finds Amanda and they run into Dave. After they inform him about Amanda's capture, they all unite to save her. Meanwhile, Medusa reminds her about her plans to use her as a hostage to escape, then she will be her personal slave to work off the lost money. Medusa estimates that in 50 years they will be even. The boys and Dave confronts Medusa and orders her ninjas to attack them, which Dave assists and fight them off before he faces her remaining mercenaries, but she incapacitates him. After the boys are able to defeat many ninjas before they catch up to her and handcuffs Amanda when shoves her one of the mercenary down, She compliments their skills, but then decides to even the odds by shooting the lights out. This gives her ninjas the upper hand because they have night vision goggles. While they are taken care of it, Medusa gives Amanda a little "surprise". Instead of being Medusa's slave, Amanda will be blown to bits by a time bomb that Medusa leaves behind and also planning to destroy the park as she escape her way back to her ship.
The boys manage to overcome their inability to see in the dark and make use of their senses (the problem with their obstacle course at the beginning with Mori's advice) and defeats the ninjas with the night vision goggles and save Amanda, but her laptop have insufficient powers that can't disarm the time bomb she's attached as they to plug it to cord, but to short-circuit. Thinking quickly, the boys attach the time bomb to an oxygen tanks and attempt to break its valve to send it away. But despite the boys' skills as ninjas, they lack the physical strength to break it. Luckily, Dave arrives and does so where they send the oxygen tank-taped time bomb off like a torpedo directly toward Medusa's escape route ship. When Medusa returns to her ship, she, her nephews and C.J. are gloats at their success. Just as Medusa is about to escape, she witness a torpedo approaching towards her ship, making Medusa, her nephews and C.J. to dive off before the timer runs off and explodes, destroying her ship on impact. The explosion draws the authorities' attention, Medusa still clutching her bag of money at the beach, but the police quickly appears and capture her, much to her distraught, who pouts and seats herself and resigns surrendering herself to the authorities.
With Medusa’s plans are foiled, Medusa and her minions were arrested and sent to prison for their crimes. The boys are hailed as heroes before they give credit to Dave for helping to save the park when interviewed by the media.