In a game of Brawl, my opponent put Marauding Raptor and Polyraptor onto the battlefield using Defense of the Heart. This results in an infinite combo unless it is disrupted. When this happened, I had Murderous Rider // Swift End in hand. When the Marauding Raptor ability (deal damage to your own creatures) went on the stack, I should have received priority to use Swift End. I don't think I clicked "resolve all" or anything, and holding full control didn't allow me to take an action.

Weirdly, after the combo went off for about 25 cycles, I got a warning message that I needed to take a different action or the game would end in a draw. Then I was suddenly able to use Swift End, but by that point, I had already lost the game, since I couldn't deal with 25+ 5/5s. In retrospect, I should have taken the draw instead of the loss, but still.