Took quite a few goes to get started but the first TaN after Vampyre eased the pressure substantially. Found a mid-late nano to build powered red armor and that sealed the deal.
Something @Omega Tyrant shared (
https://forum.chaosforge.org/index.php/topic,8862.0.html) that made a big difference:
* You only have to kill the monster with your fists. Wounding is ok (and in my mind necessary in general).
* An unmodded pistol won't kill any monster (unless you miss and hit a barrel). OT also shared that a single SOB rank or SOG won't hurt either (but it's not much point in this run).
Some things I learnt:
* Attracting attention with a pistol and then punching a monster (with Brute) from behind the doorway works well. Probably something to remember for future N! runs.
* Dodging formers bullet shots is not hard and saves a lot of damage
* Monsters who wall-slide up on you won't fire a ranged attack. For some reason I thought they did.
* If you pistol shoot a distant monster from a doorway, they'll come into the doorway (see above).
* If you pistol shoot a distant monster and then run to the doorway, they won't necessarily follow you to the door. Instead they'll wander around. Don't try to shoot them again! You might kill them.
* If you pistol shoot a former captain and you hear them use a medkit, your next shot may still kill them!
* Using a shotgun at long distance is probably ok. Probably.
Some notes about fist-only from Omega Tyrant that I wish I had known at the start:
* Meleeing a monster with a non-melee weapon will not invalidate the run
* A monster shooting at you and blowing up a barrel while you wield another weapon won't invalidate the run
* Nuking doesn't invalidate the run (unless you aren't invincible!)
And then:
* Going to the JC level and failing will invalidate your run because spawned monsters will prevent your 100% claim
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 DRL (0.9.9.8a) roguelike post-mortem character dump
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 Kantarza, level 13 Cyberdemon Colonel Marine,
 defeated the Mastermind at the City of Dis.
 He survived 89131 turns and scored 188168 points. 
 He played for 1 hour, 49 minutes and 39 seconds. 
 He wasn't afraid to be hurt plenty.
 He killed 791 out of 791 hellspawn. (100%)
 This ass-kicking marine killed all of them!
-- Special levels --------------------------------------------
  Levels generated : 11
  Levels visited   : 7
  Levels completed : 7
-- Awards ----------------------------------------------------
  Cyberdemon's Head          Killing the Cyberdemon w/o taking damage
  Medal of Prejudice         Won with 100% kills
  Shotgunnery Cross          Won & killed only with shotguns/fists
  Marksmanship Cross         Won & killed only with pistols/fists
  Sunrise Iron Fist          Won & killed only with your bare hands
  Hell Armorer Pin           Clear Hell's Armory/Deimos Lab
  Strongman Gold Badge       Win standard game using knives/fists HMP
  Strongman Platinum Badge   Win standard game using only fists HMP
  Strongman Diamond Badge    Win standard game fist-only HMP/100% kills
-- Graveyard -------------------------------------------------
  ###########################################################
  #>#####################................................####
  ######################...............####...............###
  #####################.......####.....####.....####.......##
  ####################........####.....####.....####........#
  ###################.........####.....####.....####.........
  ##################..........####..............####.........
  #################..........................................
  #################....####............................####..
  #################....####............................####..
  #################....####............................####&.
  #################....####............................####..
  #################..........................................
  ##################..........####..............####.........
  ###################.........####.....####.....####.........
  ####################......X%####.....####.....####........#
  #####################.......####.....####.....####.......##
  ######################...............####...............###
  #>#####################................................####
  ###########################################################
-- Statistics ------------------------------------------------
  Health 120/60   Experience 70708/13
  ToHit Ranged +0  ToHit Melee +6  ToDmg Ranged +0  ToDmg Melee +9
-- Traits ----------------------------------------------------
  Class : Marine
    Finesse          (Level 3)
    Tough as nails   (Level 3)
    Brute            (Level 3)
    Berserker        (Level 1)
    Badass           (Level 2)
    Vampyre          (Level 1)
  Bru->Bru->Bru->Ber->Bad->MVm->Fin->Fin->TaN->TaN->Bad->TaN->Fin->
-- Equipment -------------------------------------------------
    [a] [ Armor      ]   powered red armor [5/5] (92%)
    [b] [ Weapon     ]   nothing
    [c] [ Boots      ]   plasteel boots [2/2] (82%) (A)
    [d] [ Prepared   ]   nothing
-- Inventory -------------------------------------------------
    [a] missile launcher (6d6) [4/4]
    [b] duelist armor [2/2] (100%)
    [c] Azrael's Scythe (9d9)
    [d] large med-pack
    [e] large med-pack
    [f] large med-pack
    [g] large med-pack
    [h] large med-pack
    [i] phase device
    [j] homing phase device
    [k] homing phase device
    [l] envirosuit pack
    [m] envirosuit pack
    [n] power mod pack
    [o] power mod pack
    [p] power mod pack
    [q] technical mod pack
    [r] technical mod pack
    [s] bulk mod pack
    [t] hatred skull
    [u] tactical boots [0/0] (100%)
-- Resistances -----------------------------------------------
    bullet     - internal 60%   torso 60%   feet 60%  
    melee      - internal 60%   torso 85%   feet 60%  
    shrapnel   - internal 60%   torso 60%   feet 60%  
    acid       - internal 80%   torso 80%   feet 95%  
    fire       - internal 80%   torso 95%   feet 95%  
    plasma     - internal 80%   torso 80%   feet 80%  
-- Kills -----------------------------------------------------
    66 former humans
    88 former sergeants
    30 former captains
    64 imps
    41 demons
    312 lost souls
    32 cacodemons
    22 hell knights
    17 barons of hell
    40 arachnotrons
    9 former commandos
    19 pain elementals
    4 revenants
    18 mancubi
    9 arch-viles
    5 elite former humans
    5 elite former sergeants
    2 elite former captains
    2 bruiser brothers
    1 shambler
    1 lava elemental
    1 agony elemental
    1 Angel of Death
    1 Cyberdemon
    1 Spider Mastermind
-- History ---------------------------------------------------
  He started his journey on the surface of Phobos.
  On level 5 he stormed the Chained Court.
  On level 7 he marched into the Military Base.
  He purified his fellow comrades.
  On level 8 he encountered the Phobos Anomaly.
  On level 9 he entered Hell's Armory.
  On level 9 he found the Grammaton Cleric Beretta!
  On level 9 he found the Cybernetic Armor!
  On level 9 he assembled a tactical boots!
  He destroyed the evil within and reaped the rewards!
  On level 12 he found the City of Skulls.
  He wiped out the City of Skulls.
  On level 14 he ventured into the Spider's Lair.
  He cleared the Lair, kickin' serious spider ass!
  On level 16 he found the Tower of Babel!
  On level 19 he assembled a power armor!
  On level 19 he invaded the Unholy Cathedral!
  On level 19 he found the Azrael's Scythe!
  He then destroyed the Unholy Cathedral!
  On level 22 he entered the Lava Pits.
  He managed to clear the Lava Pits completely!
  Then at last he found Dis!
  On level 24 he finally defeated the Mastermind.
-- Messages -------------------------------------------------- 
 taste blood! 
 You hit the Spider Mastermind. You need to taste blood! 
 You hit the Spider Mastermind. The Spider Mastermind flinched! You're going 
 berserk! You need to taste blood! 
 You need to taste blood! 
 The Spider Mastermind hits you. That hurt! You're going berserk! You need to 
 taste blood! 
 You hit the Spider Mastermind. The Spider Mastermind flinched! You need to 
 taste blood! 
 You hit the Spider Mastermind. The Spider Mastermind flinched! You need to 
 taste blood! 
 You need to taste blood! 
 You need to taste blood! 
 You hit the Spider Mastermind. The Spider Mastermind dies. Congratulations! 
 You defeated the Spider Mastermind! Press <Enter>... 
 You feel relatively safe now. 
-- General --------------------------------------------------- 
 152 brave souls have ventured into Phobos:
 111 of those were killed.
 1 of those was killed by something unknown.
 2 didn't read the thermonuclear bomb manual.
 And 1 couldn't handle the stress and committed a stupid suicide.
 37 souls destroyed the Mastermind...
 2 sacrificed itself for the good of mankind.
 22 killed the bitch and survived.
 13 showed that it can outsmart Hell itself.
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