The first major battle in Super Smash Bros.. Brawl's Subspace Emissary mode forces you to choose who will live, between Princesses Peach and Zelda. The other gets turned into a statue, and can't be used until close to the end of the mode.
The real Player Punch is actually shortly after that sequence, considering the fact that soon after you save one of the princesses, Bowser attacks you and captures her anyway.
Also seeing Ness and Donkey Kong's Heroic Sacrifices to save Lucas and Diddy Kong respectively.
A more powerful Punch would be when you first encounter Master Hand in Subspace, previously the greatest force in the Smash Bros. universe, get defeated by a wave of the hand, and NOT get turned into a Trophy. He just lies there, bleeding. In a single moment, Tabuu went from some random Tron-looking guy to the most hated Nintendo character ever.
Also using his off waves to immobilize most of the characters in a single blast along with being That One Boss didn't help Tabuu's image either.
This is why it's so gratifying when Sonic the Hedgehog comes out of nowhere and destroys Tabuu's wings, which substantially weakens him so you can have a chance to finish him off.
In Dissidia 012's bonus storyline "Confessions of the Creator", you can occasionally find some of the other player characters on the world map wandering aimlessly. Talking to them will reveal they've all crossed the Despair Event Horizon big time, and will recount their own personal tale of sorrow, failure, and regret. And then occasionally after speaking to them, they'll disappear.
Mortal Kombat 9 has quite a few. One of the biggest ones being Raiden's accidental killing of Liu Kang.Shao Kahn's casual murder of Kung Lao probably counts, too. And that's not even getting into the actions of the Elder Gods.
And let's not forget the superpowered Sindel easily murdering 95% of the Earthrealm warriors in a brutal curbstomp battle. Only Johnny and Sonya survive. Oh and Sindel dies too.
JoJo's Bizarre Adventure: All Star Battle lets you inflict these on yourself in a way. KO Jonathan with Part 1 Dio's HHA? You get a frightful close up of a pained Jonathan futilely trying to block Dio's eye shot while whispering the name of his beloved Erina, just like in the original manga. Perform Johnny's GHA on Funny Valentine? You hear Johnny whispering a heartfelt thanks to Gyro, reminding you of who died to help stop Valentine. Pull off Yoshikage Kira's HHA or GHA on Shigechi and kill him with them? You hear Shigechi desperately crying out "JOOOOOOSUKEEEEEEEEEEEEEEEE!" The Dramatic Finishes are just as bad. The Morioh town finish where the hands of the dead drag the loser off to hell? Can be performed on either repulsive villains like Kars or DIO, on absolute nice guys like Jonathan or Giorno, or even on children such as Koichi or Shigechi! And if you remember what Gold Experience Requiem did to Diavolo in source, you realize that pulling it off on Jonathan or Koichi is a lot more dickish than you thought it was.
Dragonball Xenoverse 2; towards the end of the story, Towa is revealed to have put a mind control mask on the player's avatar from the last game. You then have to defeat them, but Towa does some time travelling to the moment when Trunks made the wish to summon them in the first game, effectively erasing them from existence.