TEXT: Mythos 
  Mythos​ ​is​ ​a​ ​new​ ​Skill​ ​representing​ ​a​ ​character’s​ ​knowledge​ ​of​ ​and​ ​exposure​ ​to​ ​the​ ​horrible 
  realities​ ​of​ ​Thing​ ​That​ ​Mankind​ ​Was​ ​Not​ ​Meant​ ​to​ ​Know.​ ​Unlike​ ​other​ ​skills,​ ​characters​ ​without 
  the​ ​Mythos​ ​skill​ ​are​ ​not​ ​assumed​ ​to​ ​have​ ​any​ ​significant​ ​knowledge​ ​of​ ​the​ ​Unthinkable​ ​at​ ​all, 
  and​ ​thus​ ​this​ ​skill​ ​cannot​ ​be​ ​defaulted​ ​to​ ​or​ ​used​ ​in​ ​any​ ​way​ ​until​ ​it​ ​has​ ​been​ ​raised​ ​to​ ​at​ ​least 
  Average​ ​(+1).​ ​Further,​ ​no​ ​character​ ​may​ ​begin​ ​play​ ​with​ ​this​ ​skill,​ ​nor​ ​may​ ​it​ ​be​ ​intentionally 
  advanced​ ​at​ ​Milestones.​ ​Mythos​ ​is​ ​only​ ​advanced​ ​through​ ​confrontations​ ​with​ ​the​ ​Unknowable 
  or​ ​through​ ​the​ ​careful​ ​study​ ​of​ ​a​ ​few,​ ​specific​ ​books.​ ​See​ ​the​ ​Advancement​ ​section​ ​below​ ​for 
  details. 
  ●
  Overcome:​ ​You​ ​can​ ​use​ ​the​ ​Mythos​ ​skill​ ​when​ ​forced​ ​to​ ​face​ ​the​ ​Unimaginable.​ ​When 
  presented​ ​with​ ​a​ ​non-Euclidean​ ​stairwell​ ​the​ ​seemingly​ ​goes​ ​on​ ​forever,​ ​or​ ​an​ ​unnatural 
  fog​ ​that​ ​rises​ ​up​ ​to​ ​conceal​ ​the​ ​terrors​ ​of​ ​the​ ​night,​ ​you​ ​call​ ​upon​ ​your​ ​experience​ ​with 
  the​ ​Mythos​ ​to​ ​see​ ​through​ ​the​ ​illusions​ ​of​ ​the​ ​mind​ ​and​ ​see​ ​what​ ​is​ ​really​ ​confronting 
  you. 
  ●
  Create​ ​an​ ​Advantage:​ ​You​ ​can​ ​use​ ​Mythos​ ​to​ ​draw​ ​upon​ ​your​ ​knowledge​ ​of​ ​the 
  Impossible​ ​and​ ​to​ ​help​ ​deduce​ ​whatever​ ​vulnerabilities​ ​it​ ​may​ ​have.​ ​To​ ​do​ ​this​ ​you​ ​can 
  create​ ​aspects​ ​on​ ​on​ ​yourself​ ​that​ ​indicate​ ​your​ ​ability​ ​to​ ​see​ ​past​ ​the​ ​horror​ ​of​ ​each 
  aberration​ ​or​ ​to​ ​identify​ ​some​ ​weakness​ ​in​ ​the​ ​Unfathomable​ ​thing​ ​that​ ​you​ ​are 
  confronting. 
  ●
  Attack:​ ​Mythos​ ​is​ ​not​ ​usually​ ​used​ ​to​ ​Attack. 
  ●
  Defend:​ ​Mythos​ ​is​ ​not​ ​usually​ ​used​ ​to​ ​Defend. 
  Stunts 
  ●
  Don’t​ ​look​ ​at​ ​it!:​ ​With​ ​the​ ​expenditure​ ​of​ ​a​ ​Fate​ ​Point,​ ​use​ ​Mythos​ ​to​ ​Create​ ​an 
  Advantage​ ​to​ ​help​ ​another​ ​character​ ​to​ ​see​ ​the​ ​Impossible​ ​without​ ​damaging​ ​their 
  sanity. 
  ●
  Elder​ ​Sign:​ ​Given​ ​time​ ​to​ ​inscribe​ ​the​ ​proper​ ​runes​ ​and​ ​sigils​ ​the​ ​character​ ​may​ ​use 
  Mythos​ ​to​ ​make​ ​a​ ​Defend​ ​action​ ​to​ ​stop​ ​the​ ​supernatural​ ​agents​ ​of​ ​the​ ​Inconceivable 
  from​ ​taking​ ​conflict​ ​actions​ ​against​ ​himself​ ​or​ ​a​ ​zone​ ​that​ ​he​ ​has​ ​protected.​ ​Inscribing 
  such​ ​a​ ​sign​ ​is​ ​difficult​ ​however,​ ​and​ ​doing​ ​so​ ​properly​ ​costs​ ​a​ ​Fate​ ​point. 
  ●
  Descent​ ​into​ ​Madness:​ ​The​ ​character​ ​has​ ​begun​ ​travelling​ ​a​ ​path​ ​that​ ​can​ ​only​ ​end​ ​in 
  the​ ​cost​ ​of​ ​his​ ​mind​ ​and​ ​soul.​ ​With​ ​this​ ​Stunt​ ​the​ ​character​ ​may​ ​use​ ​his​ ​Mythos​ ​skill​ ​to 
  cast​ ​any​ ​spells​ ​that​ ​he​ ​may​ ​have​ ​discovered​ ​in​ ​ancient,​ ​dusty​ ​tomes.​ ​This​ ​Stunt​ ​may​ ​be 
  taken​ ​more​ ​than​ ​once.​ ​If​ ​taken​ ​additional​ ​times​ ​it​ ​can​ ​either​ ​decrease​ ​the​ ​costs​ ​to​ ​Mental 
  Stress​ ​from​ ​spellcasting​ ​by​ ​one​ ​(to​ ​a​ ​maximum​ ​of​ ​3)​ ​or​ ​at​ ​+2​ ​to​ ​rolls​ ​to​ ​cast​ ​spells​ ​from​ ​a 
  specific​ ​tome​ ​(this​ ​benefit​ ​does​ ​not​ ​stack,​ ​though​ ​it​ ​may​ ​be​ ​taken​ ​separately​ ​for​ ​different 
  books).​ ​Not​ ​that​ ​the​ ​use​ ​of​ ​certain​ ​spells​ ​or​ ​careful​ ​study​ ​of​ ​certain​ ​tomes​ ​may​ ​require​ ​a 
  character​ ​to​ ​take​ ​this​ ​Stunt,​ ​even​ ​if​ ​it​ ​taking​ ​it​ ​an​ ​additional​ ​time​ ​would​ ​gain​ ​the​ ​character 
  no​ ​bonus​ ​or​ ​reduces​ ​his​ ​Refresh​ ​to​ ​0​ ​and​ ​removes​ ​him​ ​from​ ​play. 
  Advancement 
  
  Mythos​ ​is​ ​not​ ​purchased​ ​at​ ​creation​ ​or​ ​advanced​ ​at​ ​Milestones​ ​like​ ​other​ ​skills.​ ​Instead,​ ​points 
  in​ ​Mythos​ ​are​ ​gained​ ​by​ ​encounters​ ​with​ ​the​ ​Extraordinary​ ​which​ ​cause​ ​enough​ ​Mental​ ​Stress 
  to​ ​result​ ​in​ ​a​ ​Moderate​ ​or​ ​greater​ ​Consequence​ ​or​ ​through​ ​the​ ​careful​ ​study​ ​of​ ​Things​ ​Man​ ​Was 
  Not​ ​Meant​ ​to​ ​Know​ ​by​ ​reading​ ​forbidden​ ​books​ ​and​ ​other​ ​complex​ ​Mythos​ ​writings. 
  Special: 
  The​ ​Mythos​ ​skill​ ​lowers​ ​your​ ​ability​ ​to​ ​cope​ ​with​ ​the​ ​stresses​ ​of​ ​daily​ ​life​ ​and​ ​separate​ ​reality 
  from​ ​possibilities​ ​of​ ​the​ ​Unbelievable.​ ​As​ ​Mythos​ ​advances​ ​a​ ​character​ ​must​ ​subtract​ ​mental 
  stress​ ​boxes.​ ​Average​ ​(+1)​ ​or​ ​Fair​ ​(+2)​ ​removes​ ​the​ ​character’s​ ​highest​ ​Mental​ ​Stress​ ​box. 
  Good​ ​(+3)​ ​or​ ​Great​ ​(+4)​ ​removes​ ​the​ ​two​ ​highest​ ​Mental​ ​Stress​ ​boxes.​ ​Given​ ​enough​ ​skill​ ​or 
  practice​ ​however​ ​the​ ​character’s​ ​mind​ ​learns​ ​to​ ​work​ ​around​ ​its​ ​deficiencies​ ​however.​ ​A​ ​skill​ ​of 
  Superb​ ​(+5)​ ​and​ ​above​ ​gives​ ​him​ ​an​ ​additional​ ​Moderate​ ​Consequence​ ​slot​ ​along​ ​that​ ​can​ ​only 
  be​ ​used​ ​to​ ​offset​ ​mental​ ​harm. 
  
SOURCE: textdata/thevault/FATE (fudge) [multi]/Fate Hacks & Homebrews/Mythos skill for Fate Core.pdf