I just cursed my Pink Eye. I let my Rover die. It had lived a good life and was a little spoiled. I shrined the Pink Eye. I brought it to ranch, raised it a little until the next official E-cup tournament. I saved. I entered the battle, and lost, it got injured and died. I reset. I entered again and lost again and didn't get cursed. Reset. I battled and won, didn't get cursed. Reset. I started the battle again, lost first match, got tired and decided to give up (cancel) the other 2 matches. And voilą, it became cursed.

All that just to say that to get cursed, you don't have to win the tournament and you can save before the battle and reset. And you didn't have to mistreat the monster that died.