Inspired by the last post about good monsters, here are some cases where unsuspecting humans or humanoids become monsters.
Bratboy (MMPR - Season 3/Alien Rangers)
Rita and Zedd turned young Bulk into this monster. He poured polluted water onto the Alien Ranger when he was big. Bratboy returned back to normal at the young Power Ranger's urging and was turned back to the monster by Rita and Zedd. He told them he wouldn't do what they wanted so they turned him back to young Bulk.
Marvo the Meanie (MMPR Season 3)
Rito planned to turn the Ninja Rangers into monsters, but since he had Zedd's staff pointed the wrong way, its energy turned Mr. Wilton, a teacher that switched places with Rocky. Marvo turned all the rangers except Rocky into contaniers of liquid. When Marvo was finished by Ape Ninjazord, he turned back to Mr. Wilton.
Dimitria's alley from Inquiris was deformed and brainwashed into Divatox's servant by Porto's transformation spray. Divatox then used him to plant a detonator at the KAGV Radio Studio. He was reverted back to normal when the detonator blew up in his hand during battle. He was revived shortly after that to deliver his message to Dimitria.
When Elsa kidnaps Marty the Mackerel, he is turned into Major Mackerel. Major Mackerel uses his fishing lures to capture citizens and lure in the Power Rangers. The Power Rangers use the Z-Rex Blaster to put a stop to him. Then they access the Thundersaurus Megazord's Ankylo Drill and Parasaur Final Cut, which destroys the Major Mackerel and restores Marty the Mackerel to normal.