Sending out most fire type pokemon means that the battlefield immediately bursts into flames.
Pokemon which are prey without offense-defense measurements will not attack their predators or other prey.
Predatory pokemon (especially those who prey on humans) may attack their trainers.
You have a slew of dex entries like shedinja, spoink, and kartana that may be fatal to you or the pokemon in question
I guess pokemon can die as well, there is that ghost tower. I guess if your pokemon take enough concussions from being beaten senseless by your friend/archnemesis's gorilla, it will die.