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Tear Jerker: Kung Fu Panda: Legends of Awesomeness
How "Bad Po" treats Mr. Ping.
Po's depression after his failure leads to everyone getting kicked out of the Jade Palace in "Sight For Sore Eyes".
How the Furious Five reacted to Po messing up and getting them all kicked out was also able to swiftly bring tears about. And Tigress' tone when she blames Po...that's harsh.
The Flashback to young Shifu training with Oogway, when he believed Oogway wanted nothing to do with him in favor of Po. Also, Po discovering that among the portraits in Shifu's room was one of him and Po. The guilt over this is one of the things that sends him to bring Shifu back from his 10-Minute Retirement.
Prior to that, there's Shifu's almost childish excitement upon hearing that Po's met "Oogway's Ghost"... only for that to come crashing down in a tumble of hurt confusion when he hears his old master doesn't wish to see him. And his eventual challenging of Po and trading kernels of Oogway's wisdom that builds up to:
Po: Master Shifu just can't accept that Oogway doesn't need him anymore!
And the lead-up to the Flashback, with Shifu trudging up to the peach blossom tree and speaking to Oogway, almost begging him to appear... Really, the whole episode is one tearjerker after another.
Tigress saying good-bye to Zan in "Kung Fu Daycare". Also the earlier moment when she tells him she'll never let him out of her sight again. And the flashback to her being left at Bao Gu by her parents, then playing checkers with Shifu.
Tigress' reaction to Shifu's planned Heroic Sacrifice in "Enter The Dragon". The fact he's her adoptive father makes it even harder to watch.
The whole episode "The Master and the Panda" is full of this. Peng not only discovers that his uncle Tai Lung was killed by Po, but also that his uncle was actually pure evil and had to be killed and gives up Kung Fu out of fear of being like him. It looks like it's getting better midway, with Peng coming back to help against an empowered Temutai, only for the power to possess him and drive him nuts, with only Po strong enough to stop him. He points out that Po won't always be around to do that, and leaves forever and swears off Kung Fu so he won't become a second Tai Lung.
And Po trying so hard to reach out to Peng the whole time, even when he's angry as all get out or depressed.
In "Present Tense", Sheng Xian's daughter reacting after Tigress' negative speech about the Winter Festival, about how she has little to no family, as Tigress reflects on how much she treasures Shifu and the Five as her own unofficial family.
In "A Thousand and Twenty Questions" Master Yao reveals that one of the things Tigress really wants to know but is unwilling to ask is if Shifu is proud of her.
In "Crazy Little Ling called Love", we see how Po would react if or even when Shifu would retire. He was flat out devastated by it and was struggling not to tell the others as per Shifu's request.
Also, just how tired Shifu seem to be. The fact that he shows regret and exhaustion over the life he has led is pretty painful. He simply wants to find happiness and he took Po's words from when Ling first appeared more seriously than any of us thought.