Skulking Killer's ability triggers even if all your opponents control more than one creature. If the targeted creature's controller controls any other creatures as the ability resolves, the ability won't do anything. Notably, that player could cast a creature spell with flash or create a creature token in response to avoid the -2/-2 effect.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.