Can you give me an example of something with negative probability?

I will offer you a bet: if it doesn't happen, you have to give me a dollar, but if it does happen, you have to give me everything you own. I find it hard to believe that there's anything where that's considered good odds.

For the last, the existence of a Matrix Lord has such a large negative probability that it swamps his proffer (perhaps because it is altruistic?)

If it has such a large negative probability, wouldn't you try to avoid ever giving someone five dollars, since they anti-might be a Matrix Lord, and you can't risk a negative probability of them sparing 3^^^3 people?

Also, when you mention quantum mechanics, I think you're confusing waveform density and probability density. The waveform can be any complex number, but the probability is proportional to the square of the magnitude of the waveform. If the waveform density is 1, -1, i, or -i, the probability of seeing the particle there is the same.