"Are you pondering what I'm pondering Pinky?"
"Wuhhh... I think so, Brain, but if a ham can operate a radio, why can't a pig set a VCR?"
E.G. if I use it to reduce some monster's health from 10 to 8, but can't kill it, when it's the next players' turn, does the monster's health remain at 8 or go back up?
Goes back up. All effects of your cards last until the end of your turn at the latest.