I've never been able to intentionally cause a nightmare, even though I haven't tried much, since it hasn't been necessary. I've wanted to see how it would work out.

I think having a nightmare from which to spawn lucidity could be an easy way to have long lucid dreams. During a nightmare, the visual scene is usually extremely vivid, as is the sense of touch. In theory, this means that you don't have to spend quite as much time on stabilization, since the dream is already perfectly vivid. And, since one commonly becomes lucid right near the end of a nightmare, the dreamer could decide to either cancel or amplify the scare source, depending on the scenario and the dreamer's level of experience. Amplifying the scare source could either wake the dreamer due to sensory overload, or it could increase the intensity and already life-like clarity of the scene. This could entirely negate the need of traditional stabilization in this case. Instead, the dreamer could turn most of his/her focus to increasing lucidity to the highest possible level, and BAM! Perfect recipe for a long lucid dream.

In theory.