I was playing Crystal Chronicles (gamecube) with my younger brother (I've played it severeal times, so I know how to kill most of the bosses). I play a clavat (human, high defense fighter guy) and he plays a Yuke (weird armor-like mage guy, can turn invisible if they hold the "defend" command)
We went up against the orc king (boss for the mines). We bring his health to 1/4, triggering his self-destruct-charge-up-move (you need to kill him before he fully charges it). Due to the fact that my bro spent 10 seconds mashing the attack button when he was set on magic (which needs to be charged to use it, not mashed!), and then panicking, the boss one-hit-kills us.
The second time around, the boss triggers the attack again. I tell my brother "Ok, THIS time, we don't panic, we just mash attack and kill him before he kills us!". ...My brother doesn't listen and panics, deciding to instead turn invisible and freak out. I find myself being the only one hitting the boss, and then...*MASSIVE KABOOOOOM WITH SCREEN ZOOM!!!!*. I turn to my brother and say "DAMMIT, I told you to attack! The only way to kill that boss is to kil him before he-". And then I blink in surprise as the boss teeters over and dies, and we go to the results screen.
....Yeah, the invisibility made my brother invulnerable to the one hit kill full-screen explosion. I was shocked.