diff --git a/BopVisualEffects/Core/EffectDefinitionRegistry.cs b/BopVisualEffects/Core/EffectDefinitionRegistry.cs
index 92c05f4..ec6eabd 100644
--- a/BopVisualEffects/Core/EffectDefinitionRegistry.cs
+++ b/BopVisualEffects/Core/EffectDefinitionRegistry.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using BepInEx.Configuration;
+using BopVisualEffects.Effects.Bubble;
 using BopVisualEffects.Effects.CameraShake;
 using BopVisualEffects.Effects.CameraTilt;
 using BopVisualEffects.Effects.ColorTint;
@@ -54,6 +55,7 @@ private EffectDefinitionRegistry(string pluginGuid, ClassLogger log, ConfigFile?
 	public static void Initialize(string pluginGuid, ClassLogger log, ConfigFile config)
 	{
 		var registry = new EffectDefinitionRegistry(pluginGuid, log, config);
+		registry.Register(new BubbleEffect());
 		registry.Register(new CameraShakeEffect());
 		registry.Register(new CameraTiltEffect());
 		registry.Register(new ColorTintEffect());
diff --git a/BopVisualEffects/Effects/Bubble/BubbleEffect.cs b/BopVisualEffects/Effects/Bubble/BubbleEffect.cs
new file mode 100644
index 0000000..9599035
--- /dev/null
+++ b/BopVisualEffects/Effects/Bubble/BubbleEffect.cs
@@ -0,0 +1,332 @@
+using System.Collections.Generic;
+using BopVisualEffects.Core;
+using UnityEngine;
+using UnityEngine.Rendering;
+
+namespace BopVisualEffects.Effects.Bubble;
+
+/// <summary>
+/// Effect definition for a rising-bubble overlay.
+/// Bubbles are generated once as a fixed tileable pattern and scrolled vertically with wrapping.
+/// </summary>
+public sealed class BubbleEffect : IVisualEffectDefinition
+{
+	/// <inheritdoc />
+	public string Id => "bubble";
+
+	/// <inheritdoc />
+	public string DisplayName => "Bubble";
+
+	/// <inheritdoc />
+	public string ConfigKey => "Bubble";
+
+	/// <inheritdoc />
+	public string Description => "Renders randomly-sized bubbles rising from the bottom of the screen, fading in and out smoothly.";
+
+	/// <inheritdoc />
+	public MixtapeEventTemplate CreateTemplate(string pluginGuid)
+	{
+		return new MixtapeEventTemplate
+		{
+			dataModel = $"{pluginGuid}/{Id}",
+			length = 4.0f,
+			resizable = true,
+			properties = new Dictionary<string, object>
+			{
+				["color"] = new MixtapeEventTemplates.ColorField(new Color(0.6f, 0.85f, 1.0f, 0.5f)),
+				["count"] = 20.0f,
+				["speed"] = 0.15f,
+				["max_size"] = 0.06f
+			}
+		};
+	}
+
+	/// <inheritdoc />
+	public bool TrySchedule(Entity entity, MixtapeLoaderCustom loader)
+	{
+		var log = ClassLogger.GetForClass<BubbleEffect>();
+		var durationBeats = Mathf.Max(0.01f, entity.length);
+		var color = entity.GetColor("color");
+		var count = entity.GetFloat("count");
+		var speed = entity.GetFloat("speed");
+		var maxSize = entity.GetFloat("max_size");
+		var startBeat = entity.beat;
+		var endBeat = startBeat + durationBeats;
+
+		loader.scheduler.Schedule(startBeat, (System.Action?)SpawnAction);
+		log.Debug($"Scheduled '{DisplayName}' from beat {startBeat:0.###} to {endBeat:0.###}.");
+		return true;
+
+		void SpawnAction()
+		{
+			EffectRuntimeController.Instance.SpawnRunner<BubbleRunner>(runner =>
+				runner.Initialize(loader, loader.jukebox, startBeat, endBeat, color, count, speed, maxSize));
+		}
+	}
+
+	private sealed class BubbleRunner : MonoBehaviour
+	{
+		private bool _initialized;
+		private Color _color;
+		private int _count;
+		private float _speed;
+		private float _maxSize;
+		private float _startBeat;
+		private float _endBeat;
+		private MixtapeLoaderCustom? _loader;
+		private JukeboxScript? _jukebox;
+		private BubbleOverlay? _overlay;
+
+		/// <summary>
+		/// Initializes this runner with effect parameters.
+		/// </summary>
+		public void Initialize(MixtapeLoaderCustom loader, JukeboxScript? jukebox, float startBeat, float endBeat, Color color, float count, float speed, float maxSize)
+		{
+			_loader = loader;
+			_jukebox = jukebox;
+			_startBeat = startBeat;
+			_endBeat = endBeat;
+			_color = new Color(Mathf.Clamp01(color.r), Mathf.Clamp01(color.g), Mathf.Clamp01(color.b), Mathf.Clamp01(color.a));
+			_count = Mathf.Clamp(Mathf.RoundToInt(count), 5, 200);
+			_speed = Mathf.Max(0f, speed);
+			_maxSize = Mathf.Clamp(maxSize, 0.01f, 0.5f);
+			InitializeOverlay();
+		}
+
+		/// <summary>
+		/// Stops this effect instance.
+		/// </summary>
+		public void Stop()
+		{
+			RemoveOverlay();
+			Destroy(this);
+		}
+
+		private void LateUpdate()
+		{
+			if (_jukebox is null)
+			{
+				Stop();
+				return;
+			}
+
+			if (!_initialized)
+			{
+				InitializeOverlay();
+				if (!_initialized)
+					return;
+			}
+
+			var currentBeat = _jukebox.CurrentBeat;
+			if (currentBeat >= _endBeat)
+			{
+				Stop();
+				return;
+			}
+
+			// Fade in over first 20%, hold, fade out over last 20%.
+			var progress = Mathf.InverseLerp(_startBeat, _endBeat, currentBeat);
+			float envelope;
+			if (progress < 0.2f)
+				envelope = Mathf.InverseLerp(0f, 0.2f, progress);
+			else if (progress > 0.8f)
+				envelope = 1f - Mathf.InverseLerp(0.8f, 1f, progress);
+			else
+				envelope = 1f;
+
+			if (_overlay != null)
+				_overlay.SetParams(new Color(_color.r, _color.g, _color.b, _color.a * envelope), _count, _speed, _maxSize);
+		}
+
+		private void OnDisable()
+		{
+			RemoveOverlay();
+		}
+
+		private void InitializeOverlay()
+		{
+			Camera? camera = EffectRuntimeController.ResolveEffectCamera(_loader);
+			if (camera is null)
+				return;
+
+			_overlay = camera.gameObject.AddComponent<BubbleOverlay>();
+			_overlay.SetParams(_color, _count, _speed, _maxSize);
+			_initialized = true;
+		}
+
+		private void RemoveOverlay()
+		{
+			if (_overlay != null)
+			{
+				Destroy(_overlay);
+			}
+
+			_overlay = null;
+		}
+	}
+
+	/// <summary>
+	/// Draws rising bubble rings in OnPostRender.
+	/// Bubble positions are generated once as a fixed tileable pattern and scrolled vertically.
+	/// Must be attached to a Camera's GameObject.
+	/// </summary>
+	private sealed class BubbleOverlay : MonoBehaviour
+	{
+		private const int CircleSegments = 16;
+		private const float InnerRadiusScale = 0.7f;
+
+		private static Material? _material;
+		private Color _color;
+		private int _count;
+		private float _speed;
+		private float _maxSize;
+
+		private BubbleData[]? _bubbles;
+		private int _lastCount;
+		private float _lastMaxSize;
+
+		// Local PRNG to avoid perturbing the global UnityEngine.Random state.
+		private readonly System.Random _rng = new System.Random();
+
+		/// <summary>
+		/// Updates the overlay parameters and regenerates the bubble pattern when needed.
+		/// </summary>
+		public void SetParams(Color color, int count, float speed, float maxSize)
+		{
+			_color = color;
+			_count = count;
+			_speed = speed;
+			_maxSize = maxSize;
+
+			if (_bubbles is null || _lastCount != count || Mathf.Abs(_lastMaxSize - maxSize) > 0.0001f)
+				GenerateBubbles();
+		}
+
+		private void GenerateBubbles()
+		{
+			var minRadius = _maxSize * 0.2f;
+			_bubbles = new BubbleData[_count];
+			for (var i = 0; i < _count; i++)
+			{
+				_bubbles[i] = new BubbleData(
+					x: (float)_rng.NextDouble(),
+					y: (float)_rng.NextDouble(),
+					radius: minRadius + (float)_rng.NextDouble() * (_maxSize - minRadius));
+			}
+
+			_lastCount = _count;
+			_lastMaxSize = _maxSize;
+		}
+
+		private static Material? GetMaterial()
+		{
+			if (!_material)
+			{
+				var shader = Shader.Find("Hidden/Internal-Colored");
+				if (shader is null)
+					return null;
+
+				_material = new Material(shader) { hideFlags = HideFlags.HideAndDontSave };
+				_material.SetInt("_SrcBlend", (int)BlendMode.SrcAlpha);
+				_material.SetInt("_DstBlend", (int)BlendMode.OneMinusSrcAlpha);
+				_material.SetInt("_Cull", (int)CullMode.Off);
+				_material.SetInt("_ZWrite", 0);
+			}
+
+			return _material;
+		}
+
+		// Unity calls this on the camera's GameObject after it finishes rendering the scene.
+		private void OnPostRender()
+		{
+			if (_color.a <= 0f || _count <= 0 || _bubbles is null)
+				return;
+
+			var mat = GetMaterial();
+			if (mat is null)
+				return;
+
+			var cam = GetComponent<Camera>();
+			var aspect = (cam != null) ? cam.aspect : (16f / 9f);
+			var scrollOffset = Time.time * _speed;
+			var step = 2f * Mathf.PI / CircleSegments;
+
+			mat.SetPass(0);
+			GL.PushMatrix();
+			GL.LoadOrtho();
+			GL.Begin(GL.TRIANGLES);
+
+			foreach (var bubble in _bubbles)
+			{
+				var ry = bubble.Radius;
+				var rx = ry / aspect;
+				var cx = bubble.X;
+
+				// Scroll upward with wrapping so the pattern tiles seamlessly.
+				var cy = ((bubble.Y + scrollOffset) % 1.0f + 1.0f) % 1.0f;
+
+				DrawBubbleRing(cx, cy, rx, ry, step);
+
+				// Also draw at the adjacent vertical tile edge so bubbles don't pop when wrapping.
+				if (cy < ry)
+					DrawBubbleRing(cx, cy + 1.0f, rx, ry, step);
+				else if (cy > 1.0f - ry)
+					DrawBubbleRing(cx, cy - 1.0f, rx, ry, step);
+			}
+
+			GL.End();
+			GL.PopMatrix();
+		}
+
+		private void DrawBubbleRing(float cx, float cy, float rx, float ry, float step)
+		{
+			for (var seg = 0; seg < CircleSegments; seg++)
+			{
+				var a0 = seg * step;
+				var a1 = (seg + 1) * step;
+				var cos0 = Mathf.Cos(a0);
+				var sin0 = Mathf.Sin(a0);
+				var cos1 = Mathf.Cos(a1);
+				var sin1 = Mathf.Sin(a1);
+
+				// Outer ring vertices.
+				var ox0 = cx + cos0 * rx;
+				var oy0 = cy + sin0 * ry;
+				var ox1 = cx + cos1 * rx;
+				var oy1 = cy + sin1 * ry;
+
+				// Inner ring vertices (scaled inward to form the ring thickness).
+				var ix0 = cx + cos0 * rx * InnerRadiusScale;
+				var iy0 = cy + sin0 * ry * InnerRadiusScale;
+				var ix1 = cx + cos1 * rx * InnerRadiusScale;
+				var iy1 = cy + sin1 * ry * InnerRadiusScale;
+
+				GL.Color(_color);
+
+				// Triangle 1: outer0, outer1, inner0.
+				GL.Vertex3(ox0, oy0, 0f);
+				GL.Vertex3(ox1, oy1, 0f);
+				GL.Vertex3(ix0, iy0, 0f);
+
+				// Triangle 2: outer1, inner1, inner0.
+				GL.Vertex3(ox1, oy1, 0f);
+				GL.Vertex3(ix1, iy1, 0f);
+				GL.Vertex3(ix0, iy0, 0f);
+			}
+		}
+
+		private readonly struct BubbleData
+		{
+			public readonly float X;
+			public readonly float Y;
+			public readonly float Radius;
+
+			public BubbleData(float x, float y, float radius)
+			{
+				X = x;
+				Y = y;
+				Radius = radius;
+			}
+		}
+	}
+}
diff --git a/docs/effects/README.md b/docs/effects/README.md
index f9cb92a..3066f12 100644
--- a/docs/effects/README.md
+++ b/docs/effects/README.md
@@ -2,6 +2,25 @@
 
 This page shows the visual effects currently available in BopVisualEffects and what each one does in-game.
 
+## Bubble
+
+**DisplayName:** `Bubble`
+
+**Config Key:** `Bubble.Enabled`
+
+Renders randomly-sized bubbles rising from the bottom of the screen, fading in and out smoothly. Bubble positions are generated once as a fixed tileable pattern and scrolled vertically with wrapping for efficient rendering.
+
+**Properties**
+- `color`: Color of the bubble rings (default `#99D9FF80` — light blue, semi-transparent).
+- `count`: Number of bubbles in the pattern (5–200; default `20`).
+- `speed`: Rise speed in screen heights per second (default `0.15`).
+- `max_size`: Maximum bubble radius as a fraction of screen height (0.01–0.5; default `0.06`).
+- `length` (event length in editor): How long the effect lasts, in beats. This event is resizable in the timeline.
+
+**Preview**
+
+<!-- TODO: record preview .mp4 in-game, upload to GitHub, and replace this placeholder with the link -->
+
 ## Camera Shake
 
 **DisplayName:** `Camera Shake`