Proposed ruleset:

• In any order, defeat: Tan, Floormaster, Bee, Cif (full), 0stRanger IF Lev and Mon.
• No Special Brands, except for 0stRanger.
• Time is tracked using a real-time timer.
• Time begins after obtaining the Void Rod.
• Time ends upon reaching an ending with your current character. See other categories for details.

That's how I've been doing runs at least. Another idea is to end the timer upon defeating the last boss of your choosing.

I got the first plague knight challenge done in 9 secs