Configurable double wild battle chance, surfing double battles and flag for forcing them.

include/constants/battle_config.h

@@ -106,8 +106,12 @@
 #define B_HP_BERRIES                GEN_6 // In Gen4+, berries which restore hp activate immediately after hp drops to half. In gen3, the effect occurs at the end of the turn.
 #define B_BERRIES_INSTANT           GEN_6 // In Gen4+, most berries activate on battle start/switch-in if applicable. In gen3, they only activate either at the move end or turn end.
 
+// Flag settings. Replace the 0s with defined flags to be able to toggle the following features using those flags.
+#define B_FLAG_INVERSE_BATTLE       0 // If the flag is set, the battle's type effectiveness are inversed. For example, fire is super effective against water.
+#define B_FLAG_FORCE_DOUBLE_WILD    0 // If the flag is set, all wild battles will be double battles.
+
 // Other
-#define B_FLAG_INVERSE_BATTLE       0     // If this flag is set, the battle's type effectiveness are inversed. For example, fire is super effective against water. 0 disables the feature.
+#define B_DOUBLE_WILD_CHANCE        0     // % chance of encountering two Pokémon in a Wild Encounter.
 #define B_FAST_INTRO                TRUE  // If set to TRUE, battle intro texts print at the same time as animation of a Pokémon, as opposing to waiting for the animation to end.
 #define B_SHOW_TARGETS              TRUE  // If set to TRUE, all available targets, for moves hitting 2 or 3 Pokémon, will be shown before selecting a move.
 #define B_SLEEP_TURNS               GEN_6 // In Gen5+, sleep lasts for 1-3 turns instead of 2-5 turns.

include/wild_encounter.h

@@ -40,5 +40,6 @@ void FishingWildEncounter(u8 rod);
 u16 GetLocalWildMon(bool8 *isWaterMon);
 u16 GetLocalWaterMon(void);
 bool8 UpdateRepelCounter(void);
+bool8 TryDoDoubleWildBattle(void);
 
 #endif // GUARD_WILD_ENCOUNTER_H

src/wild_encounter.c

@@ -610,7 +610,7 @@ bool8 StandardWildEncounter(u16 currMetaTileBehavior, u16 previousMetaTileBehavi
                 // try a regular wild land encounter
                 if (TryGenerateWildMon(gWildMonHeaders[headerId].landMonsInfo, WILD_AREA_LAND, WILD_CHECK_REPEL | WILD_CHECK_KEEN_EYE) == TRUE)
                 {
-                    if (USE_BATTLE_DEBUG && !GetSafariZoneFlag() && GetMonsStateToDoubles() == PLAYER_HAS_TWO_USABLE_MONS)
+                    if (TryDoDoubleWildBattle())
                     {
                         struct Pokemon mon1 = gEnemyParty[0];
                         TryGenerateWildMon(gWildMonHeaders[headerId].landMonsInfo, WILD_AREA_LAND, WILD_CHECK_KEEN_EYE);
@@ -652,7 +652,17 @@ bool8 StandardWildEncounter(u16 currMetaTileBehavior, u16 previousMetaTileBehavi
             {
                 if (TryGenerateWildMon(gWildMonHeaders[headerId].waterMonsInfo, WILD_AREA_WATER, WILD_CHECK_REPEL | WILD_CHECK_KEEN_EYE) == TRUE)
                 {
-                    BattleSetup_StartWildBattle();
+                    if (TryDoDoubleWildBattle())
+                    {
+                        struct Pokemon mon1 = gEnemyParty[0];
+                        TryGenerateWildMon(gWildMonHeaders[headerId].waterMonsInfo, WILD_AREA_WATER, WILD_CHECK_KEEN_EYE);
+                        gEnemyParty[1] = mon1;
+                        BattleSetup_StartDoubleWildBattle();
+                    }
+                    else
+                    {
+                        BattleSetup_StartWildBattle();
+                    }
                     return TRUE;
                 }
 
@@ -957,3 +967,16 @@ static void ApplyCleanseTagEncounterRateMod(u32 *encRate)
     if (GetMonData(&gPlayerParty[0], MON_DATA_HELD_ITEM) == ITEM_CLEANSE_TAG)
         *encRate = *encRate * 2 / 3;
 }
+
+bool8 TryDoDoubleWildBattle(void)
+{
+    if (GetSafariZoneFlag() || GetMonsStateToDoubles() != PLAYER_HAS_TWO_USABLE_MONS)
+        return FALSE;
+    else if (B_FLAG_FORCE_DOUBLE_WILD != 0 && FlagGet(B_FLAG_FORCE_DOUBLE_WILD))
+        return TRUE;
+    #if B_DOUBLE_WILD_CHANCE != 0
+    else if ((Random() % 100) + 1 < B_DOUBLE_WILD_CHANCE)
+        return TRUE;
+    #endif
+    return FALSE;
+}