Robo Koopa - S1-E52
Plot hole: Near the end, Robo Koopa sets down Dr. Nerdnik after he had just captured and held him hostage. Why would he do that? (00:11:55)
Another Mother - September 30, 1981 - S2-E13
Plot hole: Sam wallops both kidnappers and rescues the son. They then leave the two child molesters unconscious beside their van. No one calls the police or has them arrested, so they're free to kidnap another kid. Sam doesn't leap until after an epilogue in which the loose ends are supposed to be resolved - but this question is left unanswered. It's not excused by a "just because we didn't see it happen doesn't mean it didn't" defense. The viewers shouldn't be left with a dangling plot hole, and one line could have cured this one.
Sukeban no me ni namida? Rûru muyou no kakutou shintaisou kecchaku - S1-E13
Plot hole: In the anime, Ranma commits an unsanctioned violation of the rules when she throws Kodachi out of the ring (the time when she gets saved from her schoolmates); she in fact grabs Kodachi's arms using legs and feet, and projects her. In the original manga there is no such mistake; Ranma used her feet to spin the club Kodachi was holding, so was not throwing Kodachi directly, but using the tool just as the rules say. (00:15:45)