Add "Extremely Easy" difficulty level

src/extra_difficulty.asm

@@ -7,16 +7,23 @@
 
 ; sizeof(DifficultyClass) == 80
 section .bss
+    ExtremelyEasyDifficultyData RESB 80
     VeryEasyDifficultyData RESB 80
     AINormalDifficultyData RESB 80
 
+sstring str_ExtremelyEasy, "ExtremelyEasy"
 sstring str_VeryEasy, "VeryEasy"
 sstring str_AINormal, "AINormal"
 sstring str_Easy, "Easy"
 
 
 ; Hack RulesClass::Difficulty to read in the new difficulty setting
 hack 0x005CE198
+    push str_ExtremelyEasy
+    mov  ecx, edi   ; CCINIClass pointer
+    mov  edx, ExtremelyEasyDifficultyData
+    call 0x005CE1E0 ; Difficulty_Get(CCINIClass & ini, DifficultyClass & diff, char const * section)
+
     push str_VeryEasy
     mov  ecx, edi   ; CCINIClass pointer
     mov  edx, VeryEasyDifficultyData
@@ -179,13 +186,26 @@ hack 0x004BB479
 
     ; Check if the requested difficulty type matches any the difficulty
     ; values that we should process
-    ; (3 = Very Easy, 1 = AINormal only if the house is an AI house)
+    ; (4 = Extremely Easy, 3 = Very Easy, 1 = AINormal only if the house is an AI house)
+    cmp  edi, 4
+    je   .Extremely_Easy_Diff
     cmp  edi, 3
     je   .Very_Easy_Diff
     cmp  edi, 1
     je   .AINormal_Diff
     jmp  .Normal_Code     ; if not, jump to original code
 
+.Extremely_Easy_Diff:
+    ; Set the 'difficulty index' of the house to 0 (Hard AI)
+    mov  dword [ecx+58h], 0
+
+    ; This difficulty level can only show up in MP
+    Set_Difficulty_Modifiers_Multiplayer ExtremelyEasyDifficultyData
+
+    mov  eax, [0x0074C488] ; RulesClass pointer
+    mov  edi, 0            ; Hard difficulty
+    jmp  0x004BB654        ; let the original game code handle the rest
+
 .Very_Easy_Diff:
 
     ; Set the 'difficulty index' of the house to 0 (Hard AI)