Floor 786, what the fuuuuuuuuuuuuuuuu.
Why did you do this? How does the enemy power scale? How many times did you save scum with emergency save?
1. I really like the idea of endless mode (starting from nothing and trying to survive as long as possible).
2. Normal enemies don't change much, they are easily defeatable even at very high floor levels.
The main issue are monster girls. They normally start with very low levels (in a normal playthrough I think can start from level 5 at max in the latest stages), but once you get to around floor 200 it becomes very hard to deal with them as they can usually kill you in a few moves (at the point I reached some of them could oneshot me effortlessly).
Another thing to mention is that you are capped to level 99 (and it happens sooner than you expect as high lvl monster girls give tons of exp) and that will be as far as you can get stronger.
The other two main ways are maxing your forging level (which takes a very long time) and getting occasional orbs from enemies (which is rare).
3. Honestly I've never lost in this run, although I've been knocked down plenty of times and I had some pretty close calls as well.
I can tell you my strats to do that if you're really interested on how I did it.
However, I had to emergency save once in a while because I played in version 0.64d and there was a very annoying bug: whenever you check your inventory and didn't see your accessory slots pop up, if you tried to equip another accessory the game would lock you out of doing anything (I think it's because the game tries to change the equipped accessory bar but it never shows up, thus making you unable to do anything).
Luckily, I've been playing the new version lately and the bug seems to have been fixed.
That is the reason I used to emergency save every now and then, other than when I logged off (this run took me like 20+ hours).