diff --git a/patches/server/0726-Add-config-for-mobs-immune-to-default-effects.patch b/patches/server/0726-Add-config-for-mobs-immune-to-default-effects.patch
new file mode 100644
index 0000000000..2db3fd9b07
--- /dev/null
+++ b/patches/server/0726-Add-config-for-mobs-immune-to-default-effects.patch
@@ -0,0 +1,83 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jake Potrebic <jake.m.potrebic@gmail.com>
+Date: Wed, 2 Dec 2020 21:03:02 -0800
+Subject: [PATCH] Add config for mobs immune to default effects
+
+
+diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+index 26e18a08a7f0bd704ff3055ce3a7814191450c85..b07368ed5b8fcacd617988d09d5d27904315cf27 100644
+--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
++++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+@@ -648,6 +648,21 @@ public class PaperWorldConfig {
+         log("Hopper Move Item Events: " + (disableHopperMoveEvents ? "disabled" : "enabled"));
+     }
+ 
++    public boolean undeadImmuneToCertainEffects = true;
++    public boolean spidersImmuneToPoisonEffect = true;
++    public boolean witherImmuneToWitherEffect = true;
++    public boolean witherSkeletonImmuneToWitherEffect = true;
++    private void mobEffectChanges() {
++        undeadImmuneToCertainEffects = getBoolean("mob-effects.undead-immune-to-certain-effects", undeadImmuneToCertainEffects);
++        log("Undead immune to harmful effects: " + undeadImmuneToCertainEffects);
++        spidersImmuneToPoisonEffect = getBoolean("mob-effects.spiders-immune-to-poison-effect", spidersImmuneToPoisonEffect);
++        log("Spiders immune to poison effect: " + spidersImmuneToPoisonEffect);
++        witherImmuneToWitherEffect = getBoolean("mob-effects.immune-to-wither-effect.wither", witherImmuneToWitherEffect);
++        log("Wither immune to wither effect: " + witherImmuneToWitherEffect);
++        witherSkeletonImmuneToWitherEffect = getBoolean("mob-effects.immune-to-wither-effect.wither-skeleton", witherSkeletonImmuneToWitherEffect);
++        log("Wither skeleton immune to wither effect: " + witherSkeletonImmuneToWitherEffect);
++    }
++
+     public boolean nerfNetherPortalPigmen = false;
+     private void nerfNetherPortalPigmen() {
+         nerfNetherPortalPigmen = getBoolean("game-mechanics.nerf-pigmen-from-nether-portals", nerfNetherPortalPigmen);
+diff --git a/src/main/java/net/minecraft/world/entity/LivingEntity.java b/src/main/java/net/minecraft/world/entity/LivingEntity.java
+index 027898e97667081840562547653d4adaeae01dda..24c629d5f26bc5aadebcf39a63930b3448525242 100644
+--- a/src/main/java/net/minecraft/world/entity/LivingEntity.java
++++ b/src/main/java/net/minecraft/world/entity/LivingEntity.java
+@@ -1133,7 +1133,7 @@ public abstract class LivingEntity extends Entity {
+         if (this.getMobType() == MobType.UNDEAD) {
+             MobEffect mobeffectlist = effect.getEffect();
+ 
+-            if (mobeffectlist == MobEffects.REGENERATION || mobeffectlist == MobEffects.POISON) {
++            if ((mobeffectlist == MobEffects.REGENERATION || mobeffectlist == MobEffects.POISON) && this.level.paperConfig.undeadImmuneToCertainEffects) { // Paper
+                 return false;
+             }
+         }
+diff --git a/src/main/java/net/minecraft/world/entity/boss/wither/WitherBoss.java b/src/main/java/net/minecraft/world/entity/boss/wither/WitherBoss.java
+index 6e3bd5146c687922e7b4680d59a1ae2d1480ad40..bb329e9c1a2295e6433d3728692a1e716c89dcc0 100644
+--- a/src/main/java/net/minecraft/world/entity/boss/wither/WitherBoss.java
++++ b/src/main/java/net/minecraft/world/entity/boss/wither/WitherBoss.java
+@@ -602,7 +602,7 @@ public class WitherBoss extends Monster implements PowerableMob, RangedAttackMob
+ 
+     @Override
+     public boolean canBeAffected(MobEffectInstance effect) {
+-        return effect.getEffect() == MobEffects.WITHER ? false : super.canBeAffected(effect);
++        return effect.getEffect() == MobEffects.WITHER && this.level.paperConfig.witherImmuneToWitherEffect ? false : super.canBeAffected(effect); // Paper
+     }
+ 
+     private class WitherDoNothingGoal extends Goal {
+diff --git a/src/main/java/net/minecraft/world/entity/monster/Spider.java b/src/main/java/net/minecraft/world/entity/monster/Spider.java
+index e5679823786f2579f93a93a5ae08ab7ae42b390c..a8162116eb888106e6f48ee836d0cc5d33b72399 100644
+--- a/src/main/java/net/minecraft/world/entity/monster/Spider.java
++++ b/src/main/java/net/minecraft/world/entity/monster/Spider.java
+@@ -133,7 +133,7 @@ public class Spider extends Monster {
+ 
+     @Override
+     public boolean canBeAffected(MobEffectInstance effect) {
+-        return effect.getEffect() == MobEffects.POISON ? false : super.canBeAffected(effect);
++        return effect.getEffect() == MobEffects.POISON && this.level.paperConfig.spidersImmuneToPoisonEffect ? false : super.canBeAffected(effect); // Paper
+     }
+ 
+     public boolean isClimbing() {
+diff --git a/src/main/java/net/minecraft/world/entity/monster/WitherSkeleton.java b/src/main/java/net/minecraft/world/entity/monster/WitherSkeleton.java
+index 033d6389e4b7d986fc63abd67e325b68a6132824..f9bc07be70fae9aced51a69bccb5eda309187a47 100644
+--- a/src/main/java/net/minecraft/world/entity/monster/WitherSkeleton.java
++++ b/src/main/java/net/minecraft/world/entity/monster/WitherSkeleton.java
+@@ -122,6 +122,6 @@ public class WitherSkeleton extends AbstractSkeleton {
+ 
+     @Override
+     public boolean canBeAffected(MobEffectInstance effect) {
+-        return effect.getEffect() == MobEffects.WITHER ? false : super.canBeAffected(effect);
++        return effect.getEffect() == MobEffects.WITHER && this.level.paperConfig.witherSkeletonImmuneToWitherEffect ? false : super.canBeAffected(effect); // Paper
+     }
+ }