First time crossing 1000 in a regular endless (have done it several times in Boss endless, which is much easier); was good enough to go further but once again was running out of time.
Here’s the build:
Because I was short of time I only recorded a few rooms, first 1005-1015, then later after the Sisu got activated, and finally when I suicided:
I reached level 25 (max) at room 833 and I was able to get the following perks from Hidden Treasures:
- Vertical Shots
- Back Shot
- Big Attack Speed Up x2
- Safety Bubble
- Adrenaline
- Titan Heart
- Fast Learner
- Titan Armour
- Fire Shots
- Balloon
- Flamethrower
- Jetpack
- Buck Shot
- Improved Poison
And got Poison Shots from the Merchant - much harder to get perks from the merchant after they disabled Haggler for endless runs 
(because of this run)