- Mutagen Man, just everything about Mutagen Man.
- The City Fall storyline is full of these, but the standout has to be Leonardo dreaming of his mother. "Hear me, child, and see... that this is no place for you."
- Mikey Leaving the family after Splinter kills shredder.
- Casey and April's Bitter breakup and the aftermath with both clearly hurting afterwords.
- The finale of Chasing Phantoms... Harold severs ties with the Turtles after his ex-wife is hurt protecting him, devastating Donnie. The Turtles' faith in Splinter is shattered when he has Darius Dunn killed despite him being defeated, causing Raph and Donnie to join Mikey in turning their back on him. When Leo asks why, Splinter reveals he did it to push them away for their own safety, knowing that he'll have to do some terrible things to keep them safe and that they're safest, and happiest, away from the Foot Clan, counting on Leo to take care of them.
- Slash's death. After they manage to break Bishop's control over him, it's revealed that the bastard implanted a nuclear bomb in Slash's body so Slash has Sally fly him over the ocean so the explosion dosen't harm anyone, Mikey even gives him one last candy bar beforehand. Afterwards the turtles and Mutanimals are devastated with Hob holding Slash's headband with tears in his eye.
- The next issue shows Michelangelo still grieving. And it doesn't help that Old Hob scoffs at his soulful eulogy and follows up with a harsh speech about how they're at war with Bishop and all others who would abuse mutants. Later, it's shown that Mikey's still sore about that, and sick of all the moral gray areas that they've found themselves in lately.
- Issue 89 has Splinter being shown his past, present and future by members of the Pantheon. The past and present both have some disheartening moments, but the future is gut-wrenching. He witnesses the direct aftermath of his sons killing him after he goes too far . The expression on Splinter's face as he begs Gothano for answers shows how terrified he is by the notion that this could be the future that his actions are leading to - or that he could end up breaking his own sons by forcing them to kill him.Splinter: NO! Please, Gothano...please tell me this is not real! Speak to me, please! This can't be real...PLEASE!
- Also in that vision, take a look at each of the Turtles' faces. Raph looks grim, Donatello resigned, Leo rueful...and Michelangelo? His expression is a blank Thousand-Yard Stare, as if part of him still can't believe that this is happening. And yet, he's still lucid enough to sadly admit that Leo did what had to be done, and that there was nothing left of the Splinter that they called father.
Tearjerker / Teenage Mutant Ninja Turtles (IDW)