The Timer!

Go get the upstairs timer. Set the timer for (5 x
players mins) and then place the timer by any
player in range. When the timer rings, it explodes
for one hundred damage.

(If a player takes longer than one minute on their
turn, add one minute to the timer. + if the player
that played this is defeated, this is disabled.)

"Everyone dreads the moment when Grandma brings
out the kitchen timer."