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 much worse than it sounds, considering that all of the characters that you befriended over the course of the game are now Brainwashed and Crazy versions of themselves that you have to fight in order to free them in The Great Maze.
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.
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.