Fanon Discontinuity: The English dub - what with censoring the ending, inferior voice acting, and changing the names - doesn't exist to most fans.
Leafie's death is completely removed in the German dub. At least with the English dub there are actually multiple versions. One incarnation completely cut the scene out while others just cut off before the One-eyed Weasel runs at her.
Fridge Brilliance: Leafie's Heroic Sacrifice at the end is very easy to understand, if you see Leafie's primary motivation as being a Mama Bear. Having seen Greenie to fledging and knowing what she did about One-Eye, she helped another mother with her babies, the only way left to her. And One-Eye knows it...she's crying when she makes the final lunge for Leafie.
Squick: The conditions in the egg-barn, and the farm ducks' habits concerning their pond.
Tear Jerker: Quite a bit. The death of Wanderer, Leafie and Greenie's goodbye, and Leafie's death stand out.
Too Dumb to Live: Debatable. One-Eye refuses to scavenge, which leads to her nearly starving herself and her pups to death, despite the fact that we first see her near a pit full of dead chickens that could have easily sustained her family.
The big question is whether or not that pit is always that full of dead chickens, more being dumped in as others putrefy. The pups are obviously very young when we see them in winter, so the weasel was obviously just hunting for herself in the spring and summer (she probably wasn't even pregnant by then) and could afford to be pickier. If there weren't as many dead chickens in the pit (and this might be the case, since the chickens had the opportunity to run off during Greenie's rescue) in winter, the ones that were there were too far decayed to be edible, or the weasel otherwise could no longer reach it, that might be where her hardship is coming from. The film never addresses this.