Those were bad but the boss battle with your avatar was worse.
The SA-X scare me terribly, but yeah, Nightmare's a tough boss.
My heart pounds when I'm against a really important opponent, and about to lose in Pokemon. Not exactly scary, but still, very tense.
This happens to me a lot, especially since I'm terrible at beating video game bosses and it takes me countless deaths before I can finally beat the boss *looks over at the stack of games I still have to beat*. I also find it humiliating that I couldn't beat the second gym leader in Pokemon Pearl without help...
Also, when I'm on a zombie server by myself in Blockland. *rounds corner and sees zombie* SHIIII---