I was reading through the large thread in the general section on TPKs within Doomsday Dawn and I started wondering how many of those deaths came from bad balancing, tough encounters, unlucky rolls, or bad choices.
So I come to the GM section to ask other GMs, what has killed your party and why was it able to? I'd like to breakdown encounters and decisions that lead to character deaths to really see what is causing it and from there discuss ways of improving that aspect of the game.
For example. During Lost Star i had a goblin rogue in the group get ambushed by the centipedes. While he took very little damage from the fight he did get poisoned by the end of it. He failed to shrug it off (DC 12) over the full course (6 rounds) of the poison and ended up dropping on the last turn. But the party was able to heal him up afterwards through the Bard and a found elixer. I was very surprised that he kept failing when he had an 11/20 chance of making the save and only managed to change the severity once. I also rolled 1s and 2s for damage pretty consistently which helped him not die but that was a major surprise to have it go the full duration.
Wennel from Rose Street Revenge. 50% because he was a NPC Cleric I played as effectively as if it were my PC, and 50% because the group was a 1st-level group who were weak on combat options. Surprisingly, my only TPK (so far) was still close, that could have gone differently if 1 or 2 dice rolls came up different.
Wennel is an interesting fight because it is a rough encounter for the PCs especially at 1st-level like you said. However the boons the PCs can use from participating in the other 3 sections can drastically change how the encounter plays out.
I think having 2 shamblers with him might have been too much for this level of encounter maybe just 1 but overall I find it to have been a tough but fair encounter.
Nobody has died in any of my games yet (though we just started chapter 5, so that's probably going to change). They came pretty close with the Lake Monster fight in Mirrored Moon (it was a combination of the high save confusion algae effectively taking the cleric out, the really high mobility/the spine rake ability, and the high monster AC). If I had kept the monster doing swim-by attacks and ranged attacks, it most certainly would have been a TPK.
Neither of my Doomsday Dawn groups have had a TPK yet. The closest they came was entirely due to trying to be too clever for their own good.