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Tear Jerker: Sonic SatAM
The Sonic Sat AM cartoon, the serious one, had several about Uncle Chuck, such as the end of Sonic Conversion, where he has his free will permanently, but still has to stay in Robotropolis.
The ending to "Spyhog". when the others learn that Uncle Chuck is staying in Robotropolis. He refuses to argue, telling them to "Get those long faces back to Knothole. I have work to do!" Then, after Sonic leaves, he hugs Bunny and Sally and tells them to take good care of his nephew. *sniff* Ocular Gushers to the max.
What about one of the earliest episodes, when they first find him and can only temporarily restore his free will with a power ring? Who could forget Sonic deperately begging his uncle to snap out of it, ignoring his friends' pleas to hurry, Bunnie having to pull him away in tears, and the poor kid crying as they flee for home?
This Yank the Dog's Chain was almost mirrored with Sally in "The Void", after finally reuniting with her father and escaping with him out of the aforementioned portal, they discover his body is dying and turning into crystal without the Void's magic and he has no choice but to return. King Acorn kisses his tearful daughter on the forehead and asks Sonic to take care of her before he is dragged into the portal. Later, back in Knothole, Sonic is left to comfort Sally, still in tears over her loss.
Bunnie's tears when her body, which had finally been turned back to flesh and blood, suddenly reverts to its cyborg form.
Any time Uncle Chuck shows up, expect it to all end in tears.
The scene when Sonic is crying after having to leave his uncle behind, especially after seeing him for the first time in years.
"Blast To The Past part 2" has several, back to back.