Endless mode is, unfortunately, A very RNG dependent game mode. You need the good combination of blitzable rooms (Rooms you can sprint without stopping) And short intro specimens... That being said, Getting less than 30 minutes might be possible in the right conditions.
I'm gonna start grinding endless to see what I can obtain.
Desirable:
- otto (Short intro, Easily Manageable, No clown)
- S1 (only in room 1-100 But short intro if lucky)
- Hyper S4 (Blitzable intro, Visual distortion tedious but can be managed, Death combo likely)
- S4 (Rooms possibly blitzable, Otherwise short intro)
- S5 (Short intro, Visual distortion easily Manageable)
- Body bag (Short intro, Easily manageable)
- Spooper (Easily manageable, Vomiting undesirable but manageable)
Undesirable:
- husk (Short intro but tedious to survive)
- Wormy (Causes blockades, Long intro)
- S12 (Long intro)
- S13 (Long intro, Constant slowness)
- S11 (Long intro, Visual distortion excessively tedious)
- S7 (Long intro but easily manageable)
- lisa (run killer)
- Ben (Time waster)
- Hangman (Time waster)
- Whiteface (Short intro, Easily Manageable. unfortunately long rooms make time constraints likely)
I will report back on my findings, I might even become number one.
edits:
- Moved white face to undesirable by recommendation of TopazstarV
I would suggest adding White face to the 'Undesirable' list - although his intro may be short, he forces you to run through extremely long rooms (the ones that make the 600s in the main part of the game a slog) for the last 15(if I remember correctly) rooms of his chase. significantly tacking onto the time it takes to get to the end of the floor - especially if you get him early on, and he re-chases you.
I did the math.
Every 100 rooms need to have a total time of 6 minutes or less, and every room needs to have a time of 3.6 seconds. If I get a short room (like the cell) then I can get a little leeway on further rooms, but if I waste too much time then the run is dead. (for comparison, sauce_dude's run had an average room time of 3.846s)