There are a lot of "fun" ways to kill someone - but I think I would go with either an injection of air into the bloodstream or an icicle to stab them to death (once it melts... no murder weapon/evidence left!)
I once heard this really creative one about pushing someone down the stairs, injecting alcohol into their bloodstream in a place were no one would notice (i.e., scalp, armpit, etc), wrapping them loosely in chains made of ice, and dumping them into the river.
This way, the person would sink with the weight of the chains, and rise to the surface once they melt. The alcohol in the bloodstream would make them look like they were drunk, and fell into the river.
However, killing somebody is not really on my "to do" list... nor will it ever be!
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