diff --git a/crates/horizon-client/src/game/native_hooks.rs b/crates/horizon-client/src/game/native_hooks.rs
index 6172256fce..d79ba7d43f 100644
--- a/crates/horizon-client/src/game/native_hooks.rs
+++ b/crates/horizon-client/src/game/native_hooks.rs
@@ -1331,6 +1331,17 @@ impl Game<'_> {
     pub(super) fn native_zoom(&self, zoom: &mut Option<NativeZoom>) {
         let _ = zoom;
     }
+    /// Final world fog, after ordinary calculations and Horizon's fog option, before upload.
+    /// Title panoramas skip it. Invalid color or distance values retain the original whole fog.
+    pub(super) fn native_render_fog(
+        &self,
+        partial: f32,
+        camera: [f64; 3],
+        fog_type: horizon_client::fog::FogType,
+        fog: &mut horizon_client::fog::FogData,
+    ) {
+        let _ = (partial, camera, fog_type, fog);
+    }
     /// The camera shake native mods ask for in this frame, `partial` ticks
     /// past the last tick (0 to 1): add your pitch, yaw and roll in degrees
     /// and your offset in blocks, along the camera's right, up and back, to
diff --git a/crates/horizon-client/src/game/render_tick.rs b/crates/horizon-client/src/game/render_tick.rs
index bc837ad9cb..345479106b 100644
--- a/crates/horizon-client/src/game/render_tick.rs
+++ b/crates/horizon-client/src/game/render_tick.rs
@@ -140,8 +140,43 @@ impl Game<'_> {
         if !self.settings.horizon.fog {
             horizon_client::fog::clear_distance_fog(&mut fog, &input);
         }
+        if self.title.is_none() {
+            fog = self.native_fog_now(self.clock.fraction() as f32, at, fog_type, fog);
+        }
         fog
     }
+    fn native_fog_now(
+        &self,
+        partial: f32,
+        camera: [f64; 3],
+        fog_type: FogType,
+        original: FogData,
+    ) -> FogData {
+        let mut fog = original;
+        self.native_render_fog(partial, camera, fog_type, &mut fog);
+        let distances = [
+            fog.environmental_start,
+            fog.environmental_end,
+            fog.render_distance_start,
+            fog.render_distance_end,
+            fog.sky_end,
+            fog.cloud_end,
+        ];
+        if fog
+            .color
+            .iter()
+            .all(|v| v.is_finite() && (0.0..=1.0).contains(v))
+            && distances.iter().all(|v| v.is_finite())
+            && fog.environmental_end > fog.environmental_start
+            && fog.render_distance_end > fog.render_distance_start
+            && fog.sky_end >= 0.0
+            && fog.cloud_end >= 0.0
+        {
+            fog
+        } else {
+            original
+        }
+    }
     /// `FogRenderer.computeFogColor`'s night vision brightenFactor:
     /// `GameRenderer.nightVisionScale`, but not while Darkness is on.
     fn fog_night_vision(&self) -> f32 {
diff --git a/tests/test_render_fog_hook.py b/tests/test_render_fog_hook.py
new file mode 100644
index 0000000000..81a8183362
--- /dev/null
+++ b/tests/test_render_fog_hook.py
@@ -0,0 +1,63 @@
+"""Exercise the actual final-fog validation/dispatch with a fake mod."""
+from pathlib import Path
+import shutil
+import subprocess
+import tempfile
+import unittest
+
+from test_world_input_capture import method
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+class RenderFogHookTests(unittest.TestCase):
+    @unittest.skipUnless(shutil.which("rustc"), "requires Rust")
+    def test_valid_parameters_and_atomic_invalid_fallback(self):
+        source = (ROOT / "crates/horizon-client/src/game/render_tick.rs").read_text(encoding="utf-8")
+        actual = method(source, "native_fog_now")
+        fixture = r"""
+#[derive(Clone, Copy)]
+enum FogType { Water }
+#[derive(Clone, Copy, Debug, PartialEq)]
+struct FogData {
+    color: [f32; 4], environmental_start: f32, environmental_end: f32,
+    render_distance_start: f32, render_distance_end: f32, sky_end: f32, cloud_end: f32,
+}
+struct Game { replacement: Option<FogData> }
+impl Game {
+    fn native_render_fog(&self, partial: f32, camera: [f64; 3], kind: FogType, fog: &mut FogData) {
+        assert_eq!((partial, camera), (0.5, [1.0, 2.0, 3.0]));
+        assert!(matches!(kind, FogType::Water));
+        assert_eq!(fog.environmental_start, -8.0);
+        if let Some(value) = self.replacement { *fog = value; }
+    }
+    METHOD
+}
+#[test]
+fn changed_unchanged_and_invalid() {
+    let original = FogData { color: [0.2, 0.3, 0.4, 1.0], environmental_start: -8.0,
+        environmental_end: 24.0, render_distance_start: 230.0, render_distance_end: 256.0,
+        sky_end: 24.0, cloud_end: 24.0 };
+    let run = |replacement| Game { replacement }.native_fog_now(0.5, [1.0, 2.0, 3.0], FogType::Water, original);
+    assert_eq!(run(None), original);
+    let changed = FogData { color: [1.0, 0.0, 0.5, 0.5], environmental_start: -16.0,
+        environmental_end: 48.0, render_distance_start: 512.0, render_distance_end: 1024.0,
+        sky_end: 0.0, cloud_end: 80.0 };
+    assert_eq!(run(Some(changed)), changed);
+    for invalid in [FogData { environmental_start: 48.0, ..changed },
+        FogData { environmental_end: f32::NAN, ..changed },
+        FogData { render_distance_end: 512.0, ..changed },
+        FogData { render_distance_start: f32::NEG_INFINITY, ..changed },
+        FogData { sky_end: -1.0, ..changed }, FogData { cloud_end: f32::INFINITY, ..changed },
+        FogData { cloud_end: -1.0, ..changed },
+        FogData { color: [f32::NAN, 0.0, 0.0, 1.0], ..changed },
+        FogData { color: [0.0, 0.0, 0.0, 1.1], ..changed }] {
+        assert_eq!(run(Some(invalid)), original);
+    }
+}
+""".replace("METHOD", actual)
+        with tempfile.TemporaryDirectory() as folder:
+            src, exe = Path(folder) / "fog.rs", Path(folder) / "fog.exe"
+            src.write_text(fixture, encoding="utf-8")
+            subprocess.run(["rustc", "--edition=2024", "--test", str(src), "-o", str(exe)], check=True)
+            subprocess.run([str(exe)], check=True)
diff --git a/tools/native-hook-fragments/render_fog.json b/tools/native-hook-fragments/render_fog.json
new file mode 100644
index 0000000000..8b3d42dda4
--- /dev/null
+++ b/tools/native-hook-fragments/render_fog.json
@@ -0,0 +1,12 @@
+{
+  "hooks": [
+    {
+      "name": "render_fog",
+      "target": "horizon_client::game::native_hooks::Game<'_>::native_render_fog",
+      "neoforge": "ViewportEvent.RenderFog",
+      "side": "client"
+    }
+  ],
+  "rust_summary": "a final world fog hook (`native_render_fog`).",
+  "doc_summary": "`native_render_fog(partial, camera, fog_type, fog)` adjusts final FogData after normal environment/effect/render-distance calculation and Horizon's fog option, before GPU upload. Title panoramas skip it. The whole request is accepted only when color components are finite in 0..=1, all distances are finite, environmental and render-distance ends exceed their starts, and sky/cloud ends are nonnegative. Negative near planes remain valid (water/lava). Invalid requests retain the original whole fog. Bundles need \"hooks\": @API:render_fog@."
+}