Not really that sad compared to the other examples(at least for you). But the episode of March of the eggxecutors from pokemon made me unhappy(also angry) because they killed Charmander by transforming him into Charizard. I felt I just got amputated when that happened. In my opinion it was a bad move, everyone must know that taking away a trait of a character will ruin the character or it will be too different. You can't make Scooby Doo brave, you can't make emperor Palpatine good, or transform Bowser into a human. Charmander seemed to be able to do awesome stuff or funny stuff, but Charizard/Charmeleon is only violent. Worst for me, I am aware that the series will always keep this ferocious pokemon and will taunt me with it as long the show continues, which is the reason I stopped watching.
Pardon me for my complaints.