diff --git a/common/src/main/java/org/embeddedt/modernfix/common/mixin/bugfix/restore_old_dragon_movement/EnderDragonMixin.java b/common/src/main/java/org/embeddedt/modernfix/common/mixin/bugfix/restore_old_dragon_movement/EnderDragonMixin.java
new file mode 100644
index 00000000..69560eb5
--- /dev/null
+++ b/common/src/main/java/org/embeddedt/modernfix/common/mixin/bugfix/restore_old_dragon_movement/EnderDragonMixin.java
@@ -0,0 +1,22 @@
+package org.embeddedt.modernfix.common.mixin.bugfix.restore_old_dragon_movement;
+
+import net.minecraft.world.entity.boss.enderdragon.EnderDragon;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.ModifyArg;
+import org.spongepowered.asm.mixin.injection.Slice;
+
+@Mixin(EnderDragon.class)
+public class EnderDragonMixin {
+    /**
+     * @author embeddedt (regression identified by Jukitsu in MC-272431)
+     * @reason Revert dragon vertical movement behavior to how it worked in 1.13 and older. Note: this patches techniques
+     * that rely on the predictable vertical descent like one-cycling.
+     */
+    @ModifyArg(method = "aiStep",
+            slice = @Slice(from = @At(value = "INVOKE", target = "Lnet/minecraft/world/entity/boss/enderdragon/phases/DragonPhaseInstance;getFlyTargetLocation()Lnet/minecraft/world/phys/Vec3;")),
+            at = @At(value = "INVOKE", target = "Lnet/minecraft/world/phys/Vec3;add(DDD)Lnet/minecraft/world/phys/Vec3;", ordinal = 0), index = 1)
+    private double fixVerticalVelocityScale(double y) {
+        return y * 10;
+    }
+}
diff --git a/common/src/main/java/org/embeddedt/modernfix/core/config/ModernFixEarlyConfig.java b/common/src/main/java/org/embeddedt/modernfix/core/config/ModernFixEarlyConfig.java
index 86532aea..3adfd91a 100644
--- a/common/src/main/java/org/embeddedt/modernfix/core/config/ModernFixEarlyConfig.java
+++ b/common/src/main/java/org/embeddedt/modernfix/core/config/ModernFixEarlyConfig.java
@@ -165,6 +165,7 @@ public class ModernFixEarlyConfig {
             .put("mixin.feature.direct_stack_trace", false)
             .put("mixin.feature.stalled_chunk_load_detection", false)
             .put("mixin.perf.blast_search_trees.force", false)
+            .put("mixin.bugfix.restore_old_dragon_movement", false)
             .put("mixin.perf.clear_mixin_classinfo", false)
             .put("mixin.perf.deduplicate_climate_parameters", false)
             .put("mixin.bugfix.packet_leak", false)
diff --git a/common/src/main/java/org/embeddedt/modernfix/world/IntegratedWatchdog.java b/common/src/main/java/org/embeddedt/modernfix/world/IntegratedWatchdog.java
index 0df35e22..8632e02c 100644
--- a/common/src/main/java/org/embeddedt/modernfix/world/IntegratedWatchdog.java
+++ b/common/src/main/java/org/embeddedt/modernfix/world/IntegratedWatchdog.java
@@ -37,6 +37,9 @@ public class IntegratedWatchdog extends Thread {
             if(!lastTickStart.isPresent()) {
                 return;
             }
+            if(lastTickStart.getAsLong() < 0) {
+                continue;
+            }
             long curTime = Util.getMillis();
             long delta = curTime - lastTickStart.getAsLong();
             if(delta > MAX_TICK_DELTA) {
diff --git a/common/src/main/resources/assets/modernfix/lang/en_us.json b/common/src/main/resources/assets/modernfix/lang/en_us.json
index 60f945d5..7964db1c 100644
--- a/common/src/main/resources/assets/modernfix/lang/en_us.json
+++ b/common/src/main/resources/assets/modernfix/lang/en_us.json
@@ -132,5 +132,6 @@
   "modernfix.option.mixin.feature.stalled_chunk_load_detection": "This option may help to detect the cause of chunkloading freezes. However, leaving it enabled may cause slightly worse performance.",
   "modernfix.option.mixin.perf.fix_loop_spin_waiting": "Fixes Minecraft's built-in wait function consuming excessive amounts of CPU resources.",
   "modernfix.option.mixin.perf.forge_cap_retrieval": "Small micro-optimization that makes retrieving custom entity data slightly more efficient on Forge.",
-  "modernfix.option.mixin.perf.forge_registry_lambda": "Fixes oversights in Forge that lead to excessive allocation in hot registry methods."
+  "modernfix.option.mixin.perf.forge_registry_lambda": "Fixes oversights in Forge that lead to excessive allocation in hot registry methods.",
+  "modernfix.option.mixin.bugfix.restore_old_dragon_movement": "Fixes MC-272431, which tracks the ender dragon being unable to dive to the portal as it did in 1.13 and older. This causes the dragon to fly quite a bit differently from what modern players are used to and also patches out one-cycling, so it's not enabled by default. Thanks to Jukitsu for identifying the regression in the vanilla code."
 }