So by this, I mean Pokémon encounters that maybe made you lose a nuzlocke, or maybe it was a shiny that got away, or a Pokémon that never let you escape no matter what... whatever it was, what was the encounter and what made it so terrible? For an example, this wasn't my encounter, but a YouTuber I was watching. He was playing a Soul Silver randomizer nuzlocke and reached the Lake of Rage. In place of Gyarados, there was a shiny Carvanha, one of his favorite water types. He switched into a Pokémon better suited to handle it, but then it used Teleport... thus, he lost the encounter.
I'll just link these images from my recent Nuzlocke attempt. Keep in mind the first one was the tutorial battle so I couldn't run. Spoiler
I was in Pokémon y, training my Charizard, victory road. I got into a horde of geodude and a shiny just so happened to be in that horde. I took a moment to gain back my barring wanted to catch it. But, like the cabrons they are, they decide it's a good idea to kill each other with magnitude. And the first one to go is the shiny. So then, I mega evolved. Killed one with flamethrower and then pulled out my Yvetal to steal their life energy, just to make sure they wouldn't get up again. And then, I saved my game, shut my DS, and sat butt hurt for a few minutes.
Thats every randomized nuzlocker's worst nightmare. I've seen that happen too many times in soullinks, especially. A terrible encounter for me was doing a semi-blind nuzlocke of Pokémon Platinum a couple of years back and finding out the hard way that Explosion halved your defense before doing damage. Rip my Toxicroak...
Wobbuffets and Randomizers. That is all. I quickly learned to try and always lead with a Ghost Type with a physical attack.
Was doing a Randomized Soul Link with a friend. It was FireRed, and we were preparing for Misty as we had struggled with getting a good team due to Soul Link rules (I had a water type starter- Crawdaunt, and my partner kept getting Water type encounters!). We went too far and decided to try getting something in Diglett's Cave. As soon as I entered our run was over- a level 15 Groudon spawned and refused to let me go as it knocked out two Pokémon with its attacks. There was also a level 31 Slowking but it let me escape... A level 21 Kadabra also took out another Pokémon in my team too. After that it was game over as we struggled grinding up weaker Pokémon and kept losing them to wild Pokémon and trainers. We probably would have survived longer if we went back from Vermilion to take on Misty but we just didn't feel secure in our teams..
It's pretty interesting. I usually play with a couple of additional rules like my mons can't be stronger than the gym leader's strongest mons, and have battle style on Set. Makes it a lot more interesting, but at the same time a lot more dangerous. Nuzlocking is where you'll find a lot of your bad moments, but that feeling when you actually win is a good feeling. Even if the only Pokémon you have remaining is a Togekiss. It also lets you appreciate certain Pokémon more than you would have in a normal playthrough.
In my Black 2 Nuzlocke, my Serperior - which was one of the strongest Pokémon on my team - was killed by a Roggenrola. This is what happens when you underestimate your opponent, kids...