Just as a follow up: I finally pulled it off.
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DoomRL (v.0.9.9.4) roguelike post-mortem character dump
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Shark, level 9 Hell Knight Sergeant Major Scout,
defeated the Cyberdemon on level 25 of the Phobos base.
He survived 92236 turns and scored 76536 points.
He played for 2 hours, 7 minutes and 16 seconds.
He didn't like it too rough.
He killed 432 out of 465 hellspawn. (92%)
He held his right to remain violent.
He was an Angel of Marksmanship!
He saved himself once.
-- Special levels --------------------------------------------
Levels generated : 10
Levels visited : 3
Levels completed : 3
-- Awards ----------------------------------------------------
Hell Armorer Badge
Hell Champion Medal
Marksman Silver Badge
-- Graveyard -------------------------------------------------
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-- Statistics ------------------------------------------------
Health 40/50 Experience 32532/9
ToHit Ranged +0 ToHit Melee +0 ToDmg Ranged +0 ToDmg Melee +0
-- Traits ----------------------------------------------------
Class : Scout
Hellrunner (Level 2)
Son of a gun (Level 2)
Dualgunner (Level 1)
Dodgemaster (Level 1)
Intuition (Level 2)
Gun Kata (Level 1)
SoG->SoG->DG->Int->Int->HR->HR->DM->MGK->
-- Equipment -------------------------------------------------
[a] [ Armor ] fireproof red armor [4/4] (90%)
[b] [ Weapon ] speedloader pistol (2d4) [6/6]
[c] [ Boots ] Enviroboots [0]
[d] [ Prepared ] high power pistol (2d7) [3/3]
-- Inventory -------------------------------------------------
[a] modified green armor [3/3] (64%) (P)
[b] red armor [4/4] (100%)
[c] plasma shield [0/0] (90%)
[d] 10mm ammo (x81)
[e] 10mm ammo (x100)
[f] 10mm ammo (x100)
[g] 10mm ammo (x100)
[h] 10mm ammo (x100)
[i] small med-pack
[j] small med-pack
[k] large med-pack
[l] large med-pack
[m] 10mm ammo chain (x250)
[n] 10mm ammo chain (x250)
[o] 10mm ammo chain (x250)
-- Resistances -----------------------------------------------
Acid - internal 0% torso 0% feet 100%
Fire - internal 0% torso 55% feet 100%
-- Kills -----------------------------------------------------
73 former humans
47 former sergeants
24 former captains
76 imps
53 demons
94 lost souls
22 cacodemons
6 barons of hell
1 Cyberdemon
8 hell knights
11 arachnotrons
3 former commandos
5 pain elementals
3 mancubi
3 revenants
2 bruiser brothers
1 shambler
-- History ---------------------------------------------------
He started his journey on the surface of Phobos.
On level 2 he assembled a speedloader pistol!
On level 3 he entered Hell's Arena.
He left the Arena as a champion!
On level 8 he assembled a tactical boots!
On level 9 he assembled a high power weapon!
On level 9 he entered Hell's Armory.
On level 9 he assembled a tactical armor!
He destroyed the evil within and reaped the rewards!
On level 10 he assembled a fireproof armor!
On level 13 he ventured into the Halls of Carnage.
On level 15 he encountered the Phobos Hellgate.
On level 18 he found the Enviroboots!
Level 21 was a hard nut to crack!
He left level 22 as soon as possible.
He left level 23 as soon as possible.
He left level 24 as soon as possible.
Then at last he found Phobos Arena!
On level 25 he finally defeated the Cyberdemon.
-- Messages --------------------------------------------------
You see : a Cyberdemon (almost dead) [m]ore | floor
The missile hits the Cyberdemon. You are hit!
The Cyberdemon reloads his rocket launcher.
Fire -- Choose target...
You see : a Cyberdemon (almost dead) [m]ore | floor
The missile hits the Cyberdemon.
You dodge! Boom!
You reload the speedloader pistol with 10mm ammo.
Fire -- Choose target...
You see : a Cyberdemon (almost dead) [m]ore | floor
The missile hits the Cyberdemon.
Fire -- Choose target...
You see : a Cyberdemon (almost dead) [m]ore | floor
The missile hits the Cyberdemon. The Cyberdemon dies. You feel
relatively safe now. Congratulations! You defeated the Cyberdemon!
Press <Enter>... You dualreload your guns!
-- General ---------------------------------------------------
77 brave souls have ventured into Phobos:
61 of those were killed.
3 didn't read the thermonuclear bomb manual.
And 5 couldn't handle the stress and committed a stupid suicide.
8 souls destroyed the Cyberdemon...
8 killed the bastard and survived.
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Oh, and yes, Gun Kata makes Cybie really easy. Step (dodge), shoot, step (dodge), shoot...
Also useful: High Power Pistol.