While I prefer a token gambling collosseum, or something like the caves quest, it’s up to you on how to proceed with the city quest!
Though I’m not sure how to balance that vault idea other than completely eliminating challenges during the quest. On diet, swarm, champions, pharma, and barren lands are lethal, but FIMA will be the worst offender as it eliminates most of the gear progression in that vault microcosm, making all melee weapons + armor useless. That “starting point” is always the most lethal in high challenges, but by the time players reach the city it’s usually a winning run already and they have the correct builds to proceed. If the city quest can even cause 20% death at this stage in the game… my biggest worry will be not experiencing the imp update entirely because skipping it becomes the optimum play on high challenges. Hope that’s not the case!
Players can prepare against tengu or caves quest to boost the winrate, but this vault quest is something that they cannot prepare against, and that constant death rate might be too unappealing as it goes against the core gameplay of “preparing for the next fight”. It might act as a fun minigame if done well, but it seems hard to execute well.
I’m not asking for the kind of progression that give permanent upgrades or starting gold to heroes. The thing is, we are already unlocking tons of “game changing” options by doing things in Shattered. We unlock characters, alchemy recipes, challenges, seeded runs. The final boss unlock might as well be another 10th challenge.
Longevity and replayability are key aspects of roguelikes and roguelites, and superbosses create a new goal for players who finished the game once. More importantly, these will create online guides, discussions, gameplay videos and reactions. This is the key for growth and momentum, and it’s one of the reasons why some roguelikes and roguelites are so successful, they have this recipe jotted down.