diff --git a/src/NosCore.GameObject/Services/BattleService/BattleStatsProvider.cs b/src/NosCore.GameObject/Services/BattleService/BattleStatsProvider.cs
index 2d273609f..c096596da 100644
--- a/src/NosCore.GameObject/Services/BattleService/BattleStatsProvider.cs
+++ b/src/NosCore.GameObject/Services/BattleService/BattleStatsProvider.cs
@@ -171,6 +171,7 @@ private static CombatStats ApplyBuffs(CombatStats stats, IReadOnlyCollection<Buf
         int defenceAll = 0, defenceMelee = 0, defenceRanged = 0, defenceMagical = 0;
         int hitRateFlat = 0, dodgeFlat = 0;
         int moraleFlat = 0;
+        int resistAll = 0, resistFire = 0, resistWater = 0, resistLight = 0, resistDark = 0;
         int elementAll = 0, elementFire = 0, elementWater = 0, elementLight = 0, elementDark = 0;
 
         foreach (var buff in buffs)
@@ -243,6 +244,22 @@ private static CombatStats ApplyBuffs(CombatStats stats, IReadOnlyCollection<Buf
                         else if (sub == (byte)AdditionalTypes.Element.DarkIncreased) elementDark += first;
                         else if (sub == (byte)AdditionalTypes.Element.DarkDecreased) elementDark -= first;
                         break;
+                    // Type 13, the defender's side of the elemental exchange. Not to be
+                    // confused with type 7 below, which is the attacker's element rate: these
+                    // four are read in ComputeElementalDamage as a percentage taken off the
+                    // incoming elemental damage.
+                    case BCardType.CardType.ElementResistance:
+                        if (sub == (byte)AdditionalTypes.ElementResistance.AllIncreased) resistAll += first;
+                        else if (sub == (byte)AdditionalTypes.ElementResistance.AllDecreased) resistAll -= first;
+                        else if (sub == (byte)AdditionalTypes.ElementResistance.FireIncreased) resistFire += first;
+                        else if (sub == (byte)AdditionalTypes.ElementResistance.FireDecreased) resistFire -= first;
+                        else if (sub == (byte)AdditionalTypes.ElementResistance.WaterIncreased) resistWater += first;
+                        else if (sub == (byte)AdditionalTypes.ElementResistance.WaterDecreased) resistWater -= first;
+                        else if (sub == (byte)AdditionalTypes.ElementResistance.LightIncreased) resistLight += first;
+                        else if (sub == (byte)AdditionalTypes.ElementResistance.LightDecreased) resistLight -= first;
+                        else if (sub == (byte)AdditionalTypes.ElementResistance.DarkIncreased) resistDark += first;
+                        else if (sub == (byte)AdditionalTypes.ElementResistance.DarkDecreased) resistDark -= first;
+                        break;
                 }
             }
         }
@@ -276,6 +293,13 @@ private static CombatStats ApplyBuffs(CombatStats stats, IReadOnlyCollection<Buf
             MagicDefence = stats.MagicDefence + defenceAll + defenceMagical,
             DefenceDodge = stats.DefenceDodge + dodgeFlat,
             DistanceDefenceDodge = stats.DistanceDefenceDodge + dodgeFlat,
+            // "All" adds to each of the four rather than living in a fifth field: the
+            // damage step reads one resistance, picked by the attacker's element, and a
+            // separate total would have to be remembered at every one of those reads.
+            FireResistance = stats.FireResistance + resistAll + resistFire,
+            WaterResistance = stats.WaterResistance + resistAll + resistWater,
+            LightResistance = stats.LightResistance + resistAll + resistLight,
+            DarkResistance = stats.DarkResistance + resistAll + resistDark,
             ElementRate = stats.ElementRate + elementFlatBonus,
         };
     }
diff --git a/test/NosCore.GameObject.Tests/Services/BattleService/ElementResistanceTests.cs b/test/NosCore.GameObject.Tests/Services/BattleService/ElementResistanceTests.cs
new file mode 100644
index 000000000..a43b19dda
--- /dev/null
+++ b/test/NosCore.GameObject.Tests/Services/BattleService/ElementResistanceTests.cs
@@ -0,0 +1,115 @@
+//  __  _  __    __   ___ __  ___ ___
+// |  \| |/__\ /' _/ / _//__\| _ \ __|
+// | | ' | \/ |`._`.| \_| \/ | v / _|
+// |_|\__|\__/ |___/ \__/\__/|_|_\___|
+//
+
+using System.Collections.Generic;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Moq;
+using NodaTime;
+using NosCore.Data.Enumerations.Buff;
+using NosCore.Data.StaticEntities;
+using NosCore.GameObject.Ecs.Interfaces;
+using NosCore.GameObject.Services.BattleService;
+using NosCore.GameObject.Services.BattleService.Model;
+
+namespace NosCore.GameObject.Tests.Services.BattleService
+{
+    // BCard type 13, "Changes elemental resistance". 561 declarations - 408 on items, 153 on
+    // cards - and the fold did not have a case for it, so a resistance buff changed nothing.
+    //
+    // The four fields it feeds are read in ComputeElementalDamage as a percentage taken off the
+    // incoming elemental damage, so getting them wrong moves numbers and raises nothing.
+    [TestClass]
+    public class ElementResistanceTests
+    {
+        private const short BaseFire = 10;
+
+        private static BCardDto Resistance(AdditionalTypes.ElementResistance subType, short value) =>
+            new()
+            {
+                Type = (byte)BCardType.CardType.ElementResistance,
+                SubType = (byte)subType,
+                FirstData = value
+            };
+
+        private static CombatStats StatsWith(params BCardDto[] bCards)
+        {
+            var monster = new NpcMonsterDto
+            {
+                FireResistance = BaseFire,
+                WaterResistance = 0,
+                LightResistance = 0,
+                DarkResistance = 0
+            };
+
+            var entity = new Mock<INonPlayableEntity>();
+            entity.SetupGet(e => e.NpcMonster).Returns(monster);
+            entity.SetupGet(e => e.Level).Returns((byte)1);
+            entity.SetupGet(e => e.HeroLevel).Returns((byte)0);
+
+            var buffs = new Mock<IBuffService>();
+            buffs.Setup(b => b.GetActiveBuffs(It.IsAny<IAliveEntity>())).Returns(new List<BuffInstance>
+            {
+                new(CardId: 1, BuffType: BuffType.Good, Caster: null,
+                    StartedAt: Instant.MinValue, ExpiresAt: Instant.MaxValue, BCards: bCards)
+            });
+
+            return new BattleStatsProvider(buffs.Object).GetStats(entity.Object);
+        }
+
+        [TestMethod]
+        public void AFireResistanceBuffAddsToTheMonstersOwn()
+        {
+            var stats = StatsWith(Resistance(AdditionalTypes.ElementResistance.FireIncreased, 25));
+
+            Assert.AreEqual(BaseFire + 25, stats.FireResistance);
+            Assert.AreEqual(0, stats.WaterResistance, "only fire was named");
+        }
+
+        // "All elemental resistance is increased by %s" reaches every one of the four. Keeping it
+        // in a fifth field would mean remembering to add it at each of the four reads.
+        [TestMethod]
+        public void TheAllSubtypeReachesEveryElement()
+        {
+            var stats = StatsWith(Resistance(AdditionalTypes.ElementResistance.AllIncreased, 15));
+
+            Assert.AreEqual(BaseFire + 15, stats.FireResistance);
+            Assert.AreEqual(15, stats.WaterResistance);
+            Assert.AreEqual(15, stats.LightResistance);
+            Assert.AreEqual(15, stats.DarkResistance);
+        }
+
+        [TestMethod]
+        public void AllAndOneElementAddUpOnThatElement()
+        {
+            var stats = StatsWith(
+                Resistance(AdditionalTypes.ElementResistance.AllIncreased, 15),
+                Resistance(AdditionalTypes.ElementResistance.WaterIncreased, 10));
+
+            Assert.AreEqual(25, stats.WaterResistance);
+            Assert.AreEqual(15, stats.LightResistance);
+        }
+
+        // The X1/X2 pairs of this type carry different sentences - "increased by" against
+        // "decreased by" - so X2 really is the negation, unlike the types where the file repeats
+        // the same line in both slots.
+        [TestMethod]
+        public void TheDecreasingSubtypeTakesAway()
+        {
+            var stats = StatsWith(Resistance(AdditionalTypes.ElementResistance.FireDecreased, 4));
+
+            Assert.AreEqual(BaseFire - 4, stats.FireResistance);
+        }
+
+        [TestMethod]
+        public void WithoutAnyOfTheseTheMonsterKeepsItsOwn()
+        {
+            var stats = StatsWith();
+
+            Assert.AreEqual(BaseFire, stats.FireResistance);
+            Assert.AreEqual(0, stats.DarkResistance);
+        }
+    }
+}