diff --git a/src/main/java/it/hurts/sskirillss/relics/config/data/StatConfigData.java b/src/main/java/it/hurts/sskirillss/relics/config/data/StatConfigData.java
index c2fd02bd..98147198 100644
--- a/src/main/java/it/hurts/sskirillss/relics/config/data/StatConfigData.java
+++ b/src/main/java/it/hurts/sskirillss/relics/config/data/StatConfigData.java
@@ -28,6 +28,7 @@ public class StatConfigData {
             MULTIPLY_BASE: x + ((x * y) * z),
             MULTIPLY_TOTAL: x * (y + 1)^z,
             ADD: x + (y * z).
+            CUSTOM: logic is overwritten in code, can't be changed via configs
             
             ...where x - Base stat value, y - Value of [upgradeModifier], z - Current relic level
             """)
diff --git a/src/main/java/it/hurts/sskirillss/relics/items/relics/base/IRelicItem.java b/src/main/java/it/hurts/sskirillss/relics/items/relics/base/IRelicItem.java
index 4dab5fb1..d3853b2e 100644
--- a/src/main/java/it/hurts/sskirillss/relics/items/relics/base/IRelicItem.java
+++ b/src/main/java/it/hurts/sskirillss/relics/items/relics/base/IRelicItem.java
@@ -43,6 +43,9 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import static it.hurts.sskirillss.relics.items.relics.base.data.leveling.misc.UpgradeOperation.*;
+
+
 public interface IRelicItem {
     @Nullable
     default Item getItem() {
@@ -886,13 +889,7 @@ default double getRelativeStatValue(String ability, String stat, double value, i
         if (data == null)
             return result;
 
-        var step = data.getUpgradeModifier().getValue();
-
-        switch (data.getUpgradeModifier().getKey()) {
-            case ADD -> result = value + (points * step);
-            case MULTIPLY_BASE -> result = value + ((value * step) * points);
-            case MULTIPLY_TOTAL -> result = value * Math.pow(step + 1, points);
-        }
+        result = data.getNewUpgradeModifier().apply(value, points);
 
         var threshold = data.getThresholdValue();
 
diff --git a/src/main/java/it/hurts/sskirillss/relics/items/relics/base/data/leveling/StatData.java b/src/main/java/it/hurts/sskirillss/relics/items/relics/base/data/leveling/StatData.java
index 5afeabc1..8832a02e 100644
--- a/src/main/java/it/hurts/sskirillss/relics/items/relics/base/data/leveling/StatData.java
+++ b/src/main/java/it/hurts/sskirillss/relics/items/relics/base/data/leveling/StatData.java
@@ -6,8 +6,11 @@
 import lombok.Data;
 import org.apache.commons.lang3.tuple.Pair;
 
+import java.util.function.BiFunction;
 import java.util.function.Function;
 
+import static it.hurts.sskirillss.relics.items.relics.base.data.leveling.misc.UpgradeOperation.CUSTOM;
+
 @Data
 @Builder
 public class StatData {
@@ -24,10 +27,11 @@ public static StatDataBuilder builder(String id) {
     @Builder.Default
     private Pair<UpgradeOperation, Double> upgradeModifier;
     @Builder.Default
+    private BiFunction<Double, Integer, Double> newUpgradeModifier;
+    @Builder.Default
     private Pair<Double, Double> initialValue;
     @Builder.Default
     private Pair<Double, Double> thresholdValue;
-
     @Builder.Default
     private Function<Double, ? extends Number> formatValue = Double::doubleValue;
 
@@ -35,8 +39,18 @@ public StatConfigData toConfigData() {
         return new StatConfigData(initialValue.getKey(), initialValue.getValue(), thresholdValue.getKey(), thresholdValue.getValue(), upgradeModifier.getKey(), upgradeModifier.getValue());
     }
 
+    public void setUpgradeModifier(Pair<UpgradeOperation, Double> upgradeModifier) {
+        this.upgradeModifier = upgradeModifier;
+        switch (upgradeModifier.getKey()) {
+            case ADD ->            newUpgradeModifier = (current, points) -> current + points * upgradeModifier.getValue();
+            case MULTIPLY_BASE ->  newUpgradeModifier = (current, points) -> current + ((current * upgradeModifier.getValue()) * points);
+            case MULTIPLY_TOTAL -> newUpgradeModifier = (current, points) -> current * Math.pow(upgradeModifier.getValue() + 1, points);
+        }
+    }
+
     public static class StatDataBuilder {
-        private Pair<UpgradeOperation, Double> upgradeModifier = Pair.of(UpgradeOperation.ADD, 0D);
+        private Pair<UpgradeOperation, Double> upgradeModifier = Pair.of(CUSTOM, 0D);
+        private BiFunction<Double, Integer, Double> newUpgradeModifier = null;
         private Pair<Double, Double> initialValue = Pair.of(0D, 0D);
         private Pair<Double, Double> thresholdValue = Pair.of(Double.MIN_VALUE, Double.MAX_VALUE);
 
@@ -58,9 +72,27 @@ public StatDataBuilder thresholdValue(double min, double max) {
             return this;
         }
 
+        private StatDataBuilder newUpgradeModifier(BiFunction<Double, Integer, Double> function) {
+            return this;
+        }
+
+        /**
+         * @deprecated Use {@code upgradeModifier(BiFunction<Double, Integer, Double> function)} instead
+         */
+        @Deprecated
         public StatDataBuilder upgradeModifier(UpgradeOperation operation, double step) {
             upgradeModifier = Pair.of(operation, step);
+            switch (operation) {
+                case ADD ->            newUpgradeModifier = (current, points) -> current + points * step;
+                case MULTIPLY_BASE ->  newUpgradeModifier = (current, points) -> current + ((current * step) * points);
+                case MULTIPLY_TOTAL -> newUpgradeModifier = (current, points) -> current * Math.pow(step + 1, points);
+            }
+
+            return this;
+        }
 
+        public StatDataBuilder upgradeModifier(BiFunction<Double, Integer, Double> function) {
+            newUpgradeModifier = function;
             return this;
         }
     }
diff --git a/src/main/java/it/hurts/sskirillss/relics/items/relics/base/data/leveling/misc/UpgradeOperation.java b/src/main/java/it/hurts/sskirillss/relics/items/relics/base/data/leveling/misc/UpgradeOperation.java
index d902ad1f..9bac95f9 100644
--- a/src/main/java/it/hurts/sskirillss/relics/items/relics/base/data/leveling/misc/UpgradeOperation.java
+++ b/src/main/java/it/hurts/sskirillss/relics/items/relics/base/data/leveling/misc/UpgradeOperation.java
@@ -1,7 +1,15 @@
 package it.hurts.sskirillss.relics.items.relics.base.data.leveling.misc;
 
+import lombok.AllArgsConstructor;
+
+/**
+ * @deprecated Use BiFunctions instead
+ */
+@Deprecated
+@AllArgsConstructor
 public enum UpgradeOperation {
     ADD,
     MULTIPLY_BASE,
-    MULTIPLY_TOTAL
+    MULTIPLY_TOTAL,
+    CUSTOM;
 }
\ No newline at end of file
diff --git a/src/main/java/it/hurts/sskirillss/relics/items/relics/belt/LeatherBeltItem.java b/src/main/java/it/hurts/sskirillss/relics/items/relics/belt/LeatherBeltItem.java
index b4279957..d5fecd21 100644
--- a/src/main/java/it/hurts/sskirillss/relics/items/relics/belt/LeatherBeltItem.java
+++ b/src/main/java/it/hurts/sskirillss/relics/items/relics/belt/LeatherBeltItem.java
@@ -39,7 +39,8 @@ public RelicData constructDefaultRelicData() {
                                 .requiredPoints(2)
                                 .stat(StatData.builder("charm")
                                         .initialValue(1D, 3D)
-                                        .upgradeModifier(UpgradeOperation.ADD, 1D)
+                                        //.upgradeModifier(UpgradeOperation.ADD, 1D) // Deprecated
+                                        .upgradeModifier(Double::sum)
                                         .formatValue(value -> (int) (MathUtils.round(value, 1)))
                                         .build())
                                 .build())