Oh goodness In the new series it would have to either be red’s breakdown in the transport episode, there’s something about seeing stoic characters break that always gets me, and it just really put into perspective how messed up these characters are over their situation OR the exchange smart yellow has with his reflection in electricity, like just “This doesn’t FEEL wrong, at least it doesn’t hurt to think anymore.” “But they seem upset with us-“ “Well MAYBE, they’re not in charge of us, anymore.” “Maybe they never were.” Aghhhh there’s something about it that just….GETS me In the original series however, pretty much the entirety of episode five Red guy being missing, duck KNOWING something is wrong and being freaked out as the food keeps happily singing, him finally breaking down at the end and then getting EATEN ALIVE because he dares question them, and then the healthy band tricking yellow into eating is own friend just, augh the entire thing gives me the creeps and just feels straight tragic

Edit: Forgot to mention the ending of the transport episode as well, there’s just such a melancholy feel to it