diff --git a/include/battle.h b/include/battle.h
index 13316eada9..8fe4fa8cce 100644
--- a/include/battle.h
+++ b/include/battle.h
@@ -600,7 +600,8 @@ struct PartyState
     u32 supersweetSyrup:1;
     u32 timesGotHit:5;
     u32 changedSpecies:11; // For forms when multiple mons can change into the same pokemon.
-    u32 padding:10;
+    u32 sentOut:1;
+    u32 padding:9;
 };
 
 // Cleared at the beginning of the battle. Fields need to be cleared when needed manually otherwise.
diff --git a/include/config/battle.h b/include/config/battle.h
index d6de6397fe..61603ba5b8 100644
--- a/include/config/battle.h
+++ b/include/config/battle.h
@@ -311,6 +311,7 @@
 #define B_TOXIC_REVERSAL                GEN_LATEST // In Gen5+, bad poison will change to regular poison at the end of battles.
 #define B_TRY_CATCH_TRAINER_BALL        GEN_LATEST // In Gen4+, trying to catch a Trainer's Pokémon does not consume the Poké Ball.
 #define B_SLEEP_CLAUSE                  FALSE      // Enables Sleep Clause all the time in every case, overriding B_FLAG_SLEEP_CLAUSE. Use that for modularity.
+#define B_PARTNER_MONS_MARKED_SEEN      FALSE      // If TRUE, if your double battle partner sends out a Pokémon you haven't encountered yet, it will be marked as SEEN in your Pokédex.
 
 #define NUM_BEEPS_GEN_LATEST            4                    // Loops 4 times
 #define NUM_BEEPS_GEN_3                 -1                   // Loops infinitely
diff --git a/include/pokemon.h b/include/pokemon.h
index ba459480e1..1e31c425b6 100644
--- a/include/pokemon.h
+++ b/include/pokemon.h
@@ -849,6 +849,7 @@ u8 GetOpposingLinkMultiBattlerId(bool8 rightSide, u8 multiplayerId);
 u16 FacilityClassToPicIndex(u16 facilityClass);
 u16 PlayerGenderToFrontTrainerPicId(u8 playerGender);
 void HandleSetPokedexFlag(enum NationalDexOrder nationalNum, u8 caseId, u32 personality);
+void HandleSetPokedexFlagFromMon(struct Pokemon *mon, u32 caseId);
 bool8 HasTwoFramesAnimation(u16 species);
 struct MonSpritesGfxManager *CreateMonSpritesGfxManager(u8 managerId, u8 mode);
 void DestroyMonSpritesGfxManager(u8 managerId);
diff --git a/src/battle_ai_switch_items.c b/src/battle_ai_switch_items.c
index 6340b921c6..ed81c19659 100644
--- a/src/battle_ai_switch_items.c
+++ b/src/battle_ai_switch_items.c
@@ -1522,7 +1522,7 @@ static u32 GetBestMonDmg(struct Pokemon *party, int firstId, int lastId, u8 inva
     return bestMonId;
 }
 
-static u32 GetFirstNonIvalidMon(u32 firstId, u32 lastId, u32 invalidMons, u32 battlerIn1, u32 battlerIn2)
+static u32 GetFirstNonInvalidMon(u32 firstId, u32 lastId, u32 invalidMons, u32 battlerIn1, u32 battlerIn2)
 {
     if (!IsDoubleBattle())
         return PARTY_SIZE;
@@ -2297,7 +2297,7 @@ static u32 GetBestMonIntegrated(struct Pokemon *party, int firstId, int lastId,
         return aceMonId;
 
     // Fallback
-    u32 bestMonId = GetFirstNonIvalidMon(firstId, lastId, invalidMons, battlerIn1, battlerIn2);
+    u32 bestMonId = GetFirstNonInvalidMon(firstId, lastId, invalidMons, battlerIn1, battlerIn2);
     if (bestMonId != PARTY_SIZE)
         return bestMonId;
 
@@ -2419,7 +2419,7 @@ u32 GetMostSuitableMonToSwitchInto(u32 battler, enum SwitchType switchType)
             return aceMonId;
 
         // Fallback
-        bestMonId = GetFirstNonIvalidMon(firstId, lastId, invalidMons, battlerIn1, battlerIn2);
+        bestMonId = GetFirstNonInvalidMon(firstId, lastId, invalidMons, battlerIn1, battlerIn2);
         if (bestMonId != PARTY_SIZE)
             return bestMonId;
 
diff --git a/src/battle_controller_opponent.c b/src/battle_controller_opponent.c
index 84b3d3c0a8..8c469733c1 100644
--- a/src/battle_controller_opponent.c
+++ b/src/battle_controller_opponent.c
@@ -567,12 +567,14 @@ static void OpponentHandleChoosePokemon(u32 battler)
             }
         }
         gBattleStruct->monToSwitchIntoId[battler] = chosenMonId;
+        GetBattlerPartyState(battler)->sentOut = TRUE;
     }
     else
     {
         chosenMonId = gBattleStruct->AI_monToSwitchIntoId[battler];
         gBattleStruct->AI_monToSwitchIntoId[battler] = PARTY_SIZE;
         gBattleStruct->monToSwitchIntoId[battler] = chosenMonId;
+        GetBattlerPartyState(battler)->sentOut = TRUE;
     }
     #if TESTING
     TestRunner_Battle_CheckSwitch(battler, chosenMonId);
diff --git a/src/battle_controller_player_partner.c b/src/battle_controller_player_partner.c
index 5426f0239f..58911f1518 100644
--- a/src/battle_controller_player_partner.c
+++ b/src/battle_controller_player_partner.c
@@ -285,7 +285,6 @@ static void PlayerPartnerHandleChoosePokemon(u32 battler)
     else if (gBattleStruct->monToSwitchIntoId[battler] >= PARTY_SIZE || !IsValidForBattle(&gPlayerParty[gBattleStruct->monToSwitchIntoId[battler]]))
     {
         chosenMonId = GetMostSuitableMonToSwitchInto(battler, SWITCH_AFTER_KO);
-
         if (chosenMonId == PARTY_SIZE || !IsValidForBattle(&gPlayerParty[chosenMonId])) // just switch to the next mon
         {
             s32 firstId = (IsAiVsAiBattle()) ? 0 : (PARTY_SIZE / 2);
@@ -303,12 +302,14 @@ static void PlayerPartnerHandleChoosePokemon(u32 battler)
             }
         }
         gBattleStruct->monToSwitchIntoId[battler] = chosenMonId;
+        GetBattlerPartyState(battler)->sentOut = TRUE;
     }
     else // Mon to switch out has been already chosen.
     {
         chosenMonId = gBattleStruct->monToSwitchIntoId[battler];
         gBattleStruct->AI_monToSwitchIntoId[battler] = PARTY_SIZE;
         gBattleStruct->monToSwitchIntoId[battler] = chosenMonId;
+        GetBattlerPartyState(battler)->sentOut = TRUE;
     }
     BtlController_EmitChosenMonReturnValue(battler, B_COMM_TO_ENGINE, chosenMonId, NULL);
     BtlController_Complete(battler);
diff --git a/src/battle_main.c b/src/battle_main.c
index c39ea52905..967520f9fb 100644
--- a/src/battle_main.c
+++ b/src/battle_main.c
@@ -3735,6 +3735,10 @@ static void DoBattleIntro(void)
             gBattleStruct->overworldWeatherDone = FALSE;
             Ai_InitPartyStruct(); // Save mons party counts, and first 2/4 mons on the battlefield.
 
+            // mark all battlers as sent out
+            for (battler = 0; battler < gBattlersCount; battler++)
+                GetBattlerPartyState(battler)->sentOut = TRUE;
+
             // Try to set a status to start the battle with
             gBattleStruct->startingStatus = 0;
             if (gBattleTypeFlags & BATTLE_TYPE_TWO_OPPONENTS && GetTrainerStartingStatusFromId(TRAINER_BATTLE_PARAM.opponentB))
@@ -5562,14 +5566,31 @@ static void HandleEndTurn_FinishBattle(void)
                         GetMonData(GetBattlerMon(battler), MON_DATA_NICKNAME, gBattleResults.playerMon2Name);
                     }
                 }
-                else if (!IsOnPlayerSide(battler))
-                {
-                    HandleSetPokedexFlag(SpeciesToNationalPokedexNum(gBattleMons[battler].species), FLAG_SET_SEEN, gBattleMons[battler].personality);
-                }
             }
             TryPutPokemonTodayOnAir();
         }
 
+        if (!(gBattleTypeFlags & (BATTLE_TYPE_LINK
+                                  | BATTLE_TYPE_EREADER_TRAINER
+                                  | BATTLE_TYPE_RECORDED_LINK
+                                  | BATTLE_TYPE_TRAINER_HILL
+                                  | BATTLE_TYPE_FRONTIER)))
+        {
+            for (u32 side = 0; side < NUM_BATTLE_SIDES; side++)
+            {
+                struct Pokemon *party = GetSideParty(side);
+
+                if (side == B_SIDE_PLAYER && !B_PARTNER_MONS_MARKED_SEEN)
+                    continue;
+
+                for (u32 partySlot = 0; partySlot < PARTY_SIZE; partySlot++)
+                {
+                    if (gBattleStruct->partyState[side][partySlot].sentOut)
+                        HandleSetPokedexFlagFromMon(&party[partySlot], FLAG_SET_SEEN);
+                }
+            }
+        }
+
         if (!(gBattleTypeFlags & (BATTLE_TYPE_LINK
                                   | BATTLE_TYPE_RECORDED_LINK
                                   | BATTLE_TYPE_TRAINER
diff --git a/src/battle_script_commands.c b/src/battle_script_commands.c
index 114da2aed7..a1b66e83f5 100755
--- a/src/battle_script_commands.c
+++ b/src/battle_script_commands.c
@@ -7176,13 +7176,7 @@ static void Cmd_switchinanim(void)
 
     battler = GetBattlerForBattleScript(cmd->battler);
 
-    if (!IsOnPlayerSide(battler)
-        && !(gBattleTypeFlags & (BATTLE_TYPE_LINK
-                                 | BATTLE_TYPE_EREADER_TRAINER
-                                 | BATTLE_TYPE_RECORDED_LINK
-                                 | BATTLE_TYPE_TRAINER_HILL
-                                 | BATTLE_TYPE_FRONTIER)))
-        HandleSetPokedexFlag(SpeciesToNationalPokedexNum(gBattleMons[battler].species), FLAG_SET_SEEN, gBattleMons[battler].personality);
+    GetBattlerPartyState(battler)->sentOut = TRUE;
 
     gAbsentBattlerFlags &= ~(1u << battler);
 
diff --git a/src/pokemon.c b/src/pokemon.c
index 61270d72c3..eb2428f2fb 100644
--- a/src/pokemon.c
+++ b/src/pokemon.c
@@ -6349,6 +6349,14 @@ void HandleSetPokedexFlag(enum NationalDexOrder nationalNum, u8 caseId, u32 pers
     }
 }
 
+void HandleSetPokedexFlagFromMon(struct Pokemon *mon, u32 caseId)
+{
+    u32 personality = GetMonData(mon, MON_DATA_PERSONALITY);
+    enum NationalDexOrder nationalNum = SpeciesToNationalPokedexNum(GetMonData(mon, MON_DATA_SPECIES));
+
+    HandleSetPokedexFlag(nationalNum, caseId, personality);
+}
+
 bool8 HasTwoFramesAnimation(u16 species)
 {
     return P_TWO_FRAME_FRONT_SPRITES