Hi GiricDeRed!
Interesting idea. This could be an easier and more attractive category for new runners.
There might be a problem though. RNG would have even bigger impact in this category when comparing to a run of the whole game. I feel like the amount of valid builds would be too limited after a couple of good runs for this to be inviting for new runners after a few submitted runs.
As an example, it would be hard for anyone to beat a run which has Dahy-Ah Kus Blessing (The demonic blessing which grants downward stab explosion) and Grubbington as a boss, since this combo would make it possible to kill the boss in seconds.
That being said, I'd probably give this a try if it were made into a category. Sounds like an interesting challenge and might work much better than I assume it would.
Maybe first boss no blessings and if that were too annoying due to knockback you could use pay for blessings daily custom mode