The finale All Gone qualifies as this. Every character dies. All of them, Marv, Pick, Rick, everyone. Except Chip. Dr. Bob's own death at the end nails it home, with him regretting everything he has done to cause the inhabitants of Klay World so much misery for such a long time as he kicks the bucket. Although it could also be considered a Heartwarming Moment, due to Chip's plan to rebuild Klay World as Clay World.
Dr. Bob: "Maybe Klay World can change... it wouldn't be the weirdest thing to happen here."