Poll

I guess it'd have to be not using magic to kill another person. Given how dangerous Harry's world is and how incredibly difficult it can be to eliminate dangers that could do some extremely, extremely awful things to other people on a large scale, I'd probably have to eventually kill someone using magic.

I don't think I'd change the past due to the butterfly effect (although I'd be tempted) and I think I could go without shape changing someone/something else. Reading minds could be useful, but it runs the risk of being extremely messy and isn't always guaranteed to bring the answers you need.

All of them, because if you break 1 you might as well break them all.

The question is of morals. If you are willing to break one then you really don't have any. So you should have another option of all of the above. It would be interesting to see how many people realize that once you break 1 you are going to break the others.

Definitely.
That's why I'd probably go with Necromancy. Might as well get the big guns out and be totally gross about it.

I'd have to say shape changing other beings because it is a non-lethal method of defense and as long as it's reversible, it'd be a fun prank. The others have too many possible repercussions.