In "Flushed But Never Forgotten," the first episode of season two of Rise of the Teenage Mutant Ninja Turtles , the brothers are haunted by a past mistake, specifically the accidental flushing of Splinter's pet goldfish, which returns as a mutated entity for revenge. This episode, which parodies I Know What You Did Last Summer , reveals the "attack" to be a lesson on honesty orchestrated by Splinter and the creature. You can watch this episode on Paramount+ . Flushed, but Never Forgotten | TMNTPedia | Fandom