My basic route:

• Climb and save at checkpoint near milly
• Hidden ending
• Load save point, do 5 heart run
• New game, get all capsules and hearts (no need to kill boss here as long as you did it flawlessly first run)

I'm actually not sure that clearing achievements is possible now that I look at it...

Remember - there's also five heart run (which could be another misc category tbh) built in.

I'd like an All Achievements category, if you think that would work. Unlock all achievements, timing ends when the final achievement notice appears (you'd have to clear them between runs)

I can write a detailed guide of any% (haven't tried 100% and probably won't, just not interesting)