Puppeteer: simple, we all know that water balloons can be filled with anything liquid. Let's take example:

"A boy fills his water balloon with gasoline with slight amount of water. After filling it, he closes it with simple turnaround knot. He then throws the water balloon (and possibly some more) to the target area. After this, he throws cigarette, tinderstick or something that is burning. What happens?"

Or then just some liquid chemicals that does not react with low level rubber, but are harmful to human skin (Like nonflamed NAPALM + additional only-water filled balloons make some nice reaction).

But if we are talking only water filled water balloons, I'd say that one could drown with one (put the balloon into one's mouth and the moment he/she inhales, destroy the balloon, which causes the water to go to the lungs.