Context: I do not understand the purpose of the design behind this Penance
If this reaches anyone who matters, I will be happy to elaborate on my experience and reflections about this topic so that I may be more concise in this intro message.
Message: I think that perhaps changing the requirement from something as tricky as killing three elites in something that causes you to go down should instead be damage based and not based by number and types of kills. If you’re going to do it by kills, do it by something that feels heroic that tells everyone what happened.
My suggestion: The penance could look like “Do X(dmg) on [difficulty] with Perils of the Warp Explosion.” That way, people know you were surrounded, and you screamed until the voices consumed you.
Or, “Kill x(unarmored/horde) on [Difficulty] with a single perils of the warp explosion.” That way, people can imagine a psyker surrounded by a horde and as s/he had been consumed by the voices there had been an explosion of warp energy leaving nothing but a crater.
Why the difference matters:
Achievement in the context of insurmountable odds, I assume the theme is meant to be in such despair that it is heroic? This penance does not feel heroic, it feels impossible, I do mission level 5s on the regular. I do not know the likelihood of this happening organically in the difficulty you suggest because this situation wouldn’t occur. Your team is either really good at wiping them out in the course of a mission, or your damage isn’t consistent and you only kill one or two with said explosion as we are taught the value of cleave, the timing would have to be … I can’t calculate it. Odds are low. The only way to easily achieve this is by having a team whose purpose is to achieve this penance. With this mindset, the gameplay and the penance do not feel organic.