Sculpin is the dark leader of the Ten Terrors. He is in charge of overseeing the that the laws of darkness are followed. His mission is ensure that the Master will rise again. He gave Necorali one of his scales to track Leanbow. Sculpin took Udonna to the underworld and was saved by Necorali and Itassis. He ultimately was defeated by Itassis in the underworld.
Black Lance is one of the most powerful Terrors. During the introduction cerimony to Briarwood, he singlehandedly takes down the Manticore Megazord in one blow. Black Lance was then sent to assist MegaHorn but he taken back into the underworld by good magic Koragg. He was destroyed by the the five Mystic Force Ranger's mystic spell seal during the final battle beetween good and evil.
Itassis is a faithful follower of the rules of darkness and won't let anything get in the way of them being followed - even if that means helping the Power Rangers. She questioned the rangers on how it was possible they could defeat them. They responded it was courage, which she ultimately used to defeat Sculpin and help the rangers defeat the Master freeing herself from the puppet's strings.
Megahorn doesn't like the rules of darkness and is sick of waiting around. He was the first to violate them. He was defeated by the Daggeron but then became a giant and was joined by Black Lance. He was finally destroyed by the Solar Streak Megazord at his weak spot Nick was in search of and Daggeron ultimately found.
Magma was the first Terror to be chosen by the Stone of Judgement. Underestimating the Rangers is what caused him to lose according to the rules of darkness and brought about his end.
Oculous is known as the cunning hunter. He has the ability to teleport using a rift between dimensions. His prime mission is to caputure the Light. He can use his lasers to demolecuralize anything in his path, but is no match for the Red Dragon Fire Ranger.
Serpentina also doesn't like the rules of darkness and gets Hekatoid to aid her cause when she finds out she'll be the next to fall prey to the rules of darkness. She captures four of the Rangers by turning into a snake and devouring them. Her plans are foiled by Itassis who reverses a spell over the Red and Pink Rangers caused by Hekatoid's interference.
Hekatoid is recruited by Serpentina to take care of the Rangers. To do this, he must disobey the rules of darkness and uses a slime to prevent the Red and Pink Rangers from morphing. He later kidnapped Udonna when she and Clare were in search of Leanbow. He had the rangers combat against duplicates of themselves. Udonna was saved by Clare, Leelee, and Phineas and was returned her ranger powers. As the white ranger, Udonna defeated Hekatoid along with the other rangers.
Gekkor explained to Necrolai the rules of darkness. Gekkor followed the Master's orders and he relentlessly followed and fought Matoombo to make sure he was the master's body. Gekkor was ultimately defeated by the Wolf Knight.
Matoombo was chosen to unleash the Master's wrath, he was gathering the city's electricty to use it against them. He was meant to be the vessel for the master but his heart got in the way. He saved a young boy and his ball from an incoming car. Vida befriended him with the boy's ball. Vida challenged him to finish her but he didn't and also destroyed the energy he had gathered. Gekkor and Itassis then questioned his actions and when Gekkor fought him. Vida and Matoombo fleed to the Sleeping Lake in the Dawn Dimension to sleep forever. As he reached it, he was done in by Sculpin. Vida watched in horror as Matoombo's body was pleaded to reveal the Master's ultimate form. He was last seen in the Rock Porium receiving DJ lessons from Vida, presumingly revived.