diff --git a/PKHeX.Core/Saves/Access/ISaveBlock5BW.cs b/PKHeX.Core/Saves/Access/ISaveBlock5BW.cs
index 583112c50..46a564bf0 100644
--- a/PKHeX.Core/Saves/Access/ISaveBlock5BW.cs
+++ b/PKHeX.Core/Saves/Access/ISaveBlock5BW.cs
@@ -15,5 +15,6 @@ public interface ISaveBlock5BW
         BattleSubway5 BattleSubway { get; }
         Entralink5 Entralink { get; }
         Musical5 Musical { get; }
+        Encount5 Encount { get; }
     }
 }
diff --git a/PKHeX.Core/Saves/Access/SaveBlockAccessor5B2W2.cs b/PKHeX.Core/Saves/Access/SaveBlockAccessor5B2W2.cs
index 8e29be6a5..310678867 100644
--- a/PKHeX.Core/Saves/Access/SaveBlockAccessor5B2W2.cs
+++ b/PKHeX.Core/Saves/Access/SaveBlockAccessor5B2W2.cs
@@ -96,6 +96,7 @@ public SaveBlockAccessor5B2W2(SAV5B2W2 sav)
             Misc = new Misc5B2W2(sav, 0x21100);
             Entralink = new Entralink5B2W2(sav, 0x21200);
             Zukan = new Zukan5(sav, 0x21400, 0x328); // form flags size is + 8 from bw with new forms (therians)
+            Encount = new Encount5B2W2(sav, 0x21900);
             BattleSubway = new BattleSubway5(sav, 0x21B00);
             PWT = new PWTBlock5(sav, 0x23700);
             Festa = new FestaBlock5(sav, 0x25900);
@@ -114,5 +115,6 @@ public SaveBlockAccessor5B2W2(SAV5B2W2 sav)
         public Entralink5 Entralink { get; }
         public FestaBlock5 Festa { get; }
         public Musical5 Musical { get; }
+        public Encount5 Encount { get; }
     }
 }
diff --git a/PKHeX.Core/Saves/Access/SaveBlockAccessor5BW.cs b/PKHeX.Core/Saves/Access/SaveBlockAccessor5BW.cs
index fb7e76bc7..76b4dbfbe 100644
--- a/PKHeX.Core/Saves/Access/SaveBlockAccessor5BW.cs
+++ b/PKHeX.Core/Saves/Access/SaveBlockAccessor5BW.cs
@@ -92,6 +92,7 @@ public SaveBlockAccessor5BW(SAV5BW sav)
             Misc = new Misc5BW(sav, 0x21200);
             Entralink = new Entralink5BW(sav, 0x21300);
             Zukan = new Zukan5(sav, 0x21600, 0x320);
+            Encount = new Encount5BW(sav, 0x21B00);
             BattleSubway = new BattleSubway5(sav, 0x21D00);
         }
 
@@ -106,5 +107,6 @@ public SaveBlockAccessor5BW(SAV5BW sav)
         public BattleSubway5 BattleSubway { get; }
         public Entralink5 Entralink { get; }
         public Musical5 Musical { get; }
+        public Encount5 Encount { get; }
     }
 }
diff --git a/PKHeX.Core/Saves/SAV3E.cs b/PKHeX.Core/Saves/SAV3E.cs
index 4c45d8fde..488bcec2c 100644
--- a/PKHeX.Core/Saves/SAV3E.cs
+++ b/PKHeX.Core/Saves/SAV3E.cs
@@ -154,6 +154,12 @@ public DecorationInventory3 Decorations
             set => SetData(Large, value.ToBytes(), 0x2734);
         }
 
+        public Swarm3 Swarm
+        {
+            get => Large.Slice(0x2B90, Swarm3.SIZE).ToClass<Swarm3>();
+            set => SetData(Large, value.ToBytesClass(), 0x2B90);
+        }
+
         protected override int MailOffset => 0x2BE0;
 
         protected override int GetDaycareEXPOffset(int slot) => GetDaycareSlotOffset(0, slot + 1) - 4; // @ end of each pkm slot
diff --git a/PKHeX.Core/Saves/SAV3RS.cs b/PKHeX.Core/Saves/SAV3RS.cs
index d357ba156..93e48b2c7 100644
--- a/PKHeX.Core/Saves/SAV3RS.cs
+++ b/PKHeX.Core/Saves/SAV3RS.cs
@@ -117,6 +117,12 @@ public DecorationInventory3 Decorations
             set => SetData(Large, value.ToBytes(), 0x26A0);
         }
 
+        public Swarm3 Swarm
+        {
+            get => Large.Slice(0x2AFC, Swarm3.SIZE).ToClass<Swarm3>();
+            set => SetData(Large, value.ToBytesClass(), 0x2AFC);
+        }
+
         protected override int MailOffset => 0x2B4C;
 
         protected override int GetDaycareEXPOffset(int slot) => GetDaycareSlotOffset(0, 2) + (2 * 0x38) + (4 * slot); // consecutive vals, after both consecutive slots & 2 mail
diff --git a/PKHeX.Core/Saves/SAV4.cs b/PKHeX.Core/Saves/SAV4.cs
index fbd93f4fd..9618ba7ac 100644
--- a/PKHeX.Core/Saves/SAV4.cs
+++ b/PKHeX.Core/Saves/SAV4.cs
@@ -534,5 +534,19 @@ public Mail4 GetMail(int mailIndex)
             int ofs = GetMailOffset(mailIndex);
             return new Mail4(GetMailData(ofs), ofs);
         }
+
+        public abstract uint SwarmSeed { get; set; }
+        public abstract uint SwarmMaxCountModulo { get; }
+
+        public uint SwarmIndex
+        {
+            get => SwarmSeed % SwarmMaxCountModulo;
+            set
+            {
+                value %= SwarmMaxCountModulo;
+                while (SwarmIndex != value)
+                    ++SwarmSeed;
+            }
+        }
     }
 }
diff --git a/PKHeX.Core/Saves/SAV4DP.cs b/PKHeX.Core/Saves/SAV4DP.cs
index d40d27a90..15f837a33 100644
--- a/PKHeX.Core/Saves/SAV4DP.cs
+++ b/PKHeX.Core/Saves/SAV4DP.cs
@@ -148,5 +148,9 @@ private void SetActiveGiftFlags(IReadOnlyList<MysteryGift> gifts)
         public override int X2 { get => BitConverter.ToUInt16(General, 0x25FA); set => BitConverter.GetBytes((ushort)value).CopyTo(General, 0x25FA); }
         public override int Y2 { get => BitConverter.ToUInt16(General, 0x25FE); set => BitConverter.GetBytes((ushort)value).CopyTo(General, 0x25FE); }
         public override int Z { get => BitConverter.ToUInt16(General, 0x2602); set => BitConverter.GetBytes((ushort)value).CopyTo(General, 0x2602); }
+
+        public override uint SafariSeed { get => BitConverter.ToUInt32(General, 0x72D0); set => BitConverter.GetBytes(value).CopyTo(General, 0x72D0); }
+        public override uint SwarmSeed { get => BitConverter.ToUInt32(General, 0x72D4); set => BitConverter.GetBytes(value).CopyTo(General, 0x72D4); }
+        public override uint SwarmMaxCountModulo => 28;
     }
 }
diff --git a/PKHeX.Core/Saves/SAV4HGSS.cs b/PKHeX.Core/Saves/SAV4HGSS.cs
index f770f0feb..413a9118c 100644
--- a/PKHeX.Core/Saves/SAV4HGSS.cs
+++ b/PKHeX.Core/Saves/SAV4HGSS.cs
@@ -234,5 +234,8 @@ public void PokeGearUnlockAllCallersNoTrainers()
         public void SetPokewalkerCoursesUnlocked(bool[] value) => ArrayUtil.SetBitFlagArray(General, OFS_WALKER + 0x8, value);
 
         public void PokewalkerCoursesSetAll(uint value = 0x07FF_FFFFu) => SetData(General, BitConverter.GetBytes(value), OFS_WALKER + 0x8);
+
+        public override uint SwarmSeed { get => BitConverter.ToUInt32(General, 0x68A8); set => BitConverter.GetBytes(value).CopyTo(General, 0x68A8); }
+        public override uint SwarmMaxCountModulo => 20;
     }
 }
diff --git a/PKHeX.Core/Saves/SAV4Pt.cs b/PKHeX.Core/Saves/SAV4Pt.cs
index 0d00e6e59..475454dbd 100644
--- a/PKHeX.Core/Saves/SAV4Pt.cs
+++ b/PKHeX.Core/Saves/SAV4Pt.cs
@@ -114,5 +114,9 @@ public override IReadOnlyList<InventoryPouch> Inventory
         public override int X2 { get => BitConverter.ToUInt16(General, 0x287E); set => BitConverter.GetBytes((ushort)value).CopyTo(General, 0x287E); }
         public override int Y2 { get => BitConverter.ToUInt16(General, 0x2882); set => BitConverter.GetBytes((ushort)value).CopyTo(General, 0x2882); }
         public override int Z { get => BitConverter.ToUInt16(General, 0x2886); set => BitConverter.GetBytes((ushort)value).CopyTo(General, 0x2886); }
+
+        public override uint SafariSeed { get => BitConverter.ToUInt32(General, 0x72D4); set => BitConverter.GetBytes(value).CopyTo(General, 0x72D4); }
+        public override uint SwarmSeed { get => BitConverter.ToUInt32(General, 0x72D8); set => BitConverter.GetBytes(value).CopyTo(General, 0x72D8); }
+        public override uint SwarmMaxCountModulo => 22;
     }
 }
diff --git a/PKHeX.Core/Saves/SAV4Sinnoh.cs b/PKHeX.Core/Saves/SAV4Sinnoh.cs
index 99e0861e6..7b9f04b02 100644
--- a/PKHeX.Core/Saves/SAV4Sinnoh.cs
+++ b/PKHeX.Core/Saves/SAV4Sinnoh.cs
@@ -182,6 +182,10 @@ private static int[] CalculateMunchlaxTrees(int tid, int sid)
         public void SetUGI_Spheres(byte[] value) => SetData(General, value, OFS_UG_Items + 0x78);
 
         #endregion
+
+        public abstract uint SafariSeed { get; set; }
+        public uint GetSafariIndex(int slot) => (SafariSeed >> (slot * 5)) & 0x1F;
+        public void SetSafariIndex(int slot, uint value) => SafariSeed = (SafariSeed & ~(0x1Fu << (slot * 5))) | (value << (slot * 5));
     }
 
     public enum PoketchColor
diff --git a/PKHeX.Core/Saves/SAV5.cs b/PKHeX.Core/Saves/SAV5.cs
index 55e4331f6..6e23eef9d 100644
--- a/PKHeX.Core/Saves/SAV5.cs
+++ b/PKHeX.Core/Saves/SAV5.cs
@@ -206,6 +206,7 @@ public EntreeForest EntreeData
         public abstract BattleSubway5 BattleSubway { get; }
         public abstract Entralink5 Entralink { get; }
         public abstract Musical5 Musical { get; }
+        public abstract Encount5 Encount { get; }
 
         public static int GetMailOffset(int index) => (index * Mail5.SIZE) + 0x1DD00;
         public byte[] GetMailData(int offset) => GetData(offset, Mail5.SIZE);
diff --git a/PKHeX.Core/Saves/SAV5B2W2.cs b/PKHeX.Core/Saves/SAV5B2W2.cs
index 2d2377133..7e7f04eb4 100644
--- a/PKHeX.Core/Saves/SAV5B2W2.cs
+++ b/PKHeX.Core/Saves/SAV5B2W2.cs
@@ -51,6 +51,7 @@ private void Initialize()
         public override BattleSubway5 BattleSubway => Blocks.BattleSubway;
         public override Entralink5 Entralink => Blocks.Entralink;
         public override Musical5 Musical => Blocks.Musical;
+        public override Encount5 Encount => Blocks.Encount;
         public FestaBlock5 Festa => Blocks.Festa;
         public PWTBlock5 PWT => Blocks.PWT;
         public override int Fused => 0x1FA00 + sizeof(uint);
diff --git a/PKHeX.Core/Saves/SAV5BW.cs b/PKHeX.Core/Saves/SAV5BW.cs
index 39c800c2a..1a5e21f27 100644
--- a/PKHeX.Core/Saves/SAV5BW.cs
+++ b/PKHeX.Core/Saves/SAV5BW.cs
@@ -51,6 +51,7 @@ private void Initialize()
         public override BattleSubway5 BattleSubway => Blocks.BattleSubway;
         public override Entralink5 Entralink => Blocks.Entralink;
         public override Musical5 Musical => Blocks.Musical;
+        public override Encount5 Encount => Blocks.Encount;
         public override int Fused => int.MinValue;
         public override int GTS => 0x20500;
     }
diff --git a/PKHeX.Core/Saves/Substructures/Gen3/IGen3Hoenn.cs b/PKHeX.Core/Saves/Substructures/Gen3/IGen3Hoenn.cs
index 4e5496e1d..8ccf96b52 100644
--- a/PKHeX.Core/Saves/Substructures/Gen3/IGen3Hoenn.cs
+++ b/PKHeX.Core/Saves/Substructures/Gen3/IGen3Hoenn.cs
@@ -9,6 +9,7 @@ public interface IGen3Hoenn
         RTC3 ClockElapsed { get; set; }
         PokeBlock3Case PokeBlocks { get; set; }
         DecorationInventory3 Decorations { get; set; }
+        Swarm3 Swarm { get; set; }
         bool HasReceivedWishmkrJirachi { get; set; }
     }
 }
diff --git a/PKHeX.Core/Saves/Substructures/Gen3/StructConverter.cs b/PKHeX.Core/Saves/Substructures/Gen3/StructConverter.cs
index 35c79bea3..26f216ceb 100644
--- a/PKHeX.Core/Saves/Substructures/Gen3/StructConverter.cs
+++ b/PKHeX.Core/Saves/Substructures/Gen3/StructConverter.cs
@@ -3,7 +3,7 @@
 
 namespace PKHeX.Core
 {
-    internal static class StructConverter
+    public static class StructConverter
     {
         public static T ToStructure<T>(this byte[] bytes) where T : struct
         {
diff --git a/PKHeX.Core/Saves/Substructures/Gen3/Swarm3.cs b/PKHeX.Core/Saves/Substructures/Gen3/Swarm3.cs
new file mode 100644
index 000000000..1cd743748
--- /dev/null
+++ b/PKHeX.Core/Saves/Substructures/Gen3/Swarm3.cs
@@ -0,0 +1,23 @@
+using System.Runtime.InteropServices;
+
+namespace PKHeX.Core
+{
+    [StructLayout(LayoutKind.Sequential, Pack = 4, Size = SIZE)]
+    public sealed class Swarm3
+    {
+        public const int SIZE = 0x14;
+
+        public ushort Species { get; set; }
+        public byte MapNum { get; set; }
+        public byte MapGroup { get; set; }
+        public byte Level { get; set; }
+        // 3byte align
+        public ushort Move1 { get; set; }
+        public ushort Move2 { get; set; }
+        public ushort Move3 { get; set; }
+        public ushort Move4 { get; set; }
+        public byte Zero { get; set; }
+        public byte EncounterProbability { get; set; }
+        public ushort DaysLeft { get; set; }
+    }
+}
diff --git a/PKHeX.Core/Saves/Substructures/Gen5/Encount5.cs b/PKHeX.Core/Saves/Substructures/Gen5/Encount5.cs
new file mode 100644
index 000000000..adccff1af
--- /dev/null
+++ b/PKHeX.Core/Saves/Substructures/Gen5/Encount5.cs
@@ -0,0 +1,39 @@
+using System;
+
+namespace PKHeX.Core
+{
+    public abstract class Encount5 : SaveBlock
+    {
+        protected Encount5(SAV5 SAV, int offset) : base(SAV) => Offset = offset;
+
+        public abstract uint SwarmSeed { get; set; }
+        public abstract uint SwarmMaxCountModulo { get; }
+
+        public uint SwarmIndex
+        {
+            get => SwarmSeed % SwarmMaxCountModulo;
+            set
+            {
+                value %= SwarmMaxCountModulo;
+                while (SwarmIndex != value)
+                    ++SwarmSeed;
+            }
+        }
+    }
+
+    public sealed class Encount5BW : Encount5
+    {
+        public Encount5BW(SAV5BW SAV, int offset) : base(SAV, offset) { }
+
+        public override uint SwarmSeed { get => BitConverter.ToUInt32(Data, Offset + 0x30); set => BitConverter.GetBytes(value).CopyTo(Data, Offset + 0x30); }
+        public override uint SwarmMaxCountModulo => 17;
+    }
+
+    public sealed class Encount5B2W2 : Encount5
+    {
+        public Encount5B2W2(SAV5B2W2 SAV, int offset) : base(SAV, offset) { }
+
+        public override uint SwarmSeed { get => BitConverter.ToUInt32(Data, Offset + 0x2C); set => BitConverter.GetBytes(value).CopyTo(Data, Offset + 0x2C); }
+        public override uint SwarmMaxCountModulo => 19;
+    }
+}
diff --git a/PKHeX.Core/Saves/Substructures/Gen5/Entralink5.cs b/PKHeX.Core/Saves/Substructures/Gen5/Entralink5.cs
index 73c5d5ecd..11f329b6c 100644
--- a/PKHeX.Core/Saves/Substructures/Gen5/Entralink5.cs
+++ b/PKHeX.Core/Saves/Substructures/Gen5/Entralink5.cs
@@ -19,37 +19,6 @@ public ushort BlackCityLevel
         }
     }
 
-    public sealed class Musical5 : SaveBlock
-    {
-        public Musical5(SAV5BW SAV, int offset) : base(SAV) => Offset = offset;
-        public Musical5(SAV5B2W2 SAV, int offset) : base(SAV) => Offset = offset;
-
-        private const int PropOffset = 0x258;
-
-        public void UnlockAllMusicalProps()
-        {
-            // 101 props, which is 12.X bytes of bitflags.
-            var bitFieldOffset = Offset + PropOffset;
-            for (int i = 0; i < 0xC; i++)
-                Data[bitFieldOffset + i] = 0xFF;
-            Data[bitFieldOffset + 0xC] = 0x1F; // top 3 bits unset, to complete multiple of 8 (101=>104 bits).
-        }
-
-        public bool GetHasProp(int prop)
-        {
-            var bitFieldOffset = Offset + PropOffset;
-            var bitOffset = prop >> 3;
-            return SAV.GetFlag(bitFieldOffset + bitOffset, prop & 7);
-        }
-
-        public void SetHasProp(int prop, bool value = true)
-        {
-            var bitFieldOffset = Offset + PropOffset;
-            var bitOffset = prop >> 3;
-            SAV.SetFlag(bitFieldOffset + bitOffset, prop & 7, value);
-        }
-    }
-
     public sealed class Entralink5BW : Entralink5
     {
         public Entralink5BW(SAV5BW SAV, int offset) : base(SAV, offset) { }
diff --git a/PKHeX.Core/Saves/Substructures/Gen5/Musical5.cs b/PKHeX.Core/Saves/Substructures/Gen5/Musical5.cs
new file mode 100644
index 000000000..314130837
--- /dev/null
+++ b/PKHeX.Core/Saves/Substructures/Gen5/Musical5.cs
@@ -0,0 +1,33 @@
+namespace PKHeX.Core
+{
+    public sealed class Musical5 : SaveBlock
+    {
+        public Musical5(SAV5BW SAV, int offset) : base(SAV) => Offset = offset;
+        public Musical5(SAV5B2W2 SAV, int offset) : base(SAV) => Offset = offset;
+
+        private const int PropOffset = 0x258;
+
+        public void UnlockAllMusicalProps()
+        {
+            // 101 props, which is 12.X bytes of bitflags.
+            var bitFieldOffset = Offset + PropOffset;
+            for (int i = 0; i < 0xC; i++)
+                Data[bitFieldOffset + i] = 0xFF;
+            Data[bitFieldOffset + 0xC] = 0x1F; // top 3 bits unset, to complete multiple of 8 (101=>104 bits).
+        }
+
+        public bool GetHasProp(int prop)
+        {
+            var bitFieldOffset = Offset + PropOffset;
+            var bitOffset = prop >> 3;
+            return SAV.GetFlag(bitFieldOffset + bitOffset, prop & 7);
+        }
+
+        public void SetHasProp(int prop, bool value = true)
+        {
+            var bitFieldOffset = Offset + PropOffset;
+            var bitOffset = prop >> 3;
+            SAV.SetFlag(bitFieldOffset + bitOffset, prop & 7, value);
+        }
+    }
+}
diff --git a/Tests/PKHeX.Core.Tests/General/MarshalTests.cs b/Tests/PKHeX.Core.Tests/General/MarshalTests.cs
new file mode 100644
index 000000000..a028f2381
--- /dev/null
+++ b/Tests/PKHeX.Core.Tests/General/MarshalTests.cs
@@ -0,0 +1,21 @@
+using FluentAssertions;
+using PKHeX.Core;
+using Xunit;
+
+namespace PKHeX.Tests.General
+{
+    public class MarshalTests
+    {
+        [Fact]
+        public void MarshalStructure()
+        {
+            new DecorationInventory3().ToBytes().Length.Should().Be(DecorationInventory3.SIZE);
+        }
+
+        [Fact]
+        public void MarshalClass()
+        {
+            new Swarm3().ToBytesClass().Length.Should().Be(Swarm3.SIZE);
+        }
+    }
+}