During "Legendary Catastros" watching Nick get over his fear of Catastros and managing to help the wounded beast.
In "Ranger Down", Phineas finding and adopting an abandoned Fireheart, it's best when Fireheart starts calling him "Daddy".
Jenji staying well-past his time limit to try to help the Rangers against the Monster of the Week and risking vanishing forever.
Madison: Jenji, why didn't you go back to Rootcore and save yourself? Jenji: You guys are my family... my only family. Tell Fireheart I'm sorry.
Near the end of "Heir Apparent Pt. 2" when Udonna reveals to Koragg/Leanbow that he's Nicks father, and her husband. Koragg stands their stunned for a second, then in a moment of clarity reaches out to his son. It's cheesy, it's Narmish true, but it's still a very heartwarming scene.
"Mystic Fate Pt. 1", after the master has possessed Nick, he forces Nick to don Koragg's armor and attack innocent creatures. Eventually Nick is talked down by his father much in the same way Udonna did for him, this manages to break him free of the Master's Mind Control.
Boy: (gives Matoombo his ball and pats him on the head before leaving) Okay.
Watching several of the series villians getting along well with the rangers including a revived Matoombo.
Also, watching Itassis bombarding Daggeron with questions.
The friendship formed between the comic-relief characters of Claire, Leelee and Phineas, especially when Claire and Phineas very quickly warm up to Reformed, but Rejected Leelee and give her a chance, which helps convince the Rangers to finally do the same.
A meta example: Using the late Machiko Soga's footage as Magiel to portray "Mystic Mother", and stating in-universe that she had formerly been Rita Repulsa before reforming.