The absolute lowest time currently obtainable is 11:08.
However, as the game has become more complex and broken, there are frame perfect tricks that could greatly lower the time.
Looking at all possible walls to make game lag less.
16 different rocket jumps.
9 ghost wall tricks (Frame perfect??).
If all executed, and timed correctly, with first try every trick... it could see a run in sub 11 time.
Ghost Wall 1
Finding another way into the exit from behind would be a holy grail. For now, you have to ghost wall into the blue key door room. level can be finished in less then 42 seconds at lowest.
This level is a pain with shot gunners. Don't get flustered by them. the rocket on this level is a one and done, if you fail.. the next level set up isn't possible for sub 11.
Keep area you are going to towards opposite side of screen you are going towards. 'I go left, so keep level area in right side of view'. Turning left and right helps while passing 'Sectors' of levels.
Ghost Wall 2 & 3
This trick is a nightmare, I had gotten the ghost wall near the switch before in the 3DO and atari Jaguar Versions, but this was the first time it ever happened on GBA.
You drop into another plane by keeping the plane you want to land in over your ammo and armor counter. turn left and right before hitting the invisible barriers.
Usually the fastest possible way is to get into the room with the zombie men near the exit, which will be needed for sub 11.
E1M8 Boss Skip
Ghost Wall 4
This trick I thought would never work in a run.
You need to turn and shoot. hold strafe and backwards walk at the same time. you only go through both walls sometimes. This is a run killer.
Pretty standard route since conception. Rocketing out from where the blue armor is saves just under 10 second, but can possibly fail with an unwanted double wall jump. AKA, run killer.
This level can be a run killer if you fail to get more then 75 health by the time you rocket jump.
Ghost wall 5
THIS IS THE EASIEST GHOST WALL TO PRACTICE.
Right at the beginning, you rocket and head for the ghost wall to the left side of the level. 26 seconds is the lowest time for any% for now, with first try on the ghost wall.
You can rocket in the tunnel or by the berserk power up.
Recommend 60 health or more for set up in E2M8
Get invulnerability. Grab 100 health.
Grab Armor and Health, Rocket
Ghost Wall 6
Get to the corner in the 3rd room. A double ghost wall into the exit room is possible, for a 6 second time.
Ghost Wall 7
This was the first ghost wall level discovered.
Ghost Wall 8
The key here is to not stay on the lava sector, and end up dead after the rocket. Chain gun or shot gun come in handy for ghost walls.
Rocket 14, 15, 16
Ghost Wall 9
The Hardest trick in the game. Having just over 196 health and 196 armor make it possible to triple rocket jump. This trick ruined 4 different 11 pace runs, before I was finally able to get enough luck to pull it off for the sub 12.
I'll get more in depth with the route at another time, but all of these tricks would require first try to get below 11... so its going to be an insane play when it happens!