TO SQUASH: Nuke ball explosion.

Assets/Scripts/Game/Balls/BallBase.cs

@@ -199,4 +199,9 @@ public class BallBase : MonoBehaviour
         bounds = default;
         return false;
     }
+
+    public void StopBall()
+    {
+        speed = new Vector2(0.0f, 0.0f);
+    }
 }

Assets/Scripts/Game/Balls/NukeBall.cs

@@ -1,4 +1,6 @@
 using UnityEngine;
+using System.Collections;
+using System.Collections.Generic;
 
 public class NukeBall : BallBase
 {
@@ -6,6 +8,8 @@ public class NukeBall : BallBase
 
     public AudioClip explosionSound;
 
+    public GameObject explosionEffectPrefab;
+
     public WorldFiller worldFiller;
 
     // Tracks escalating danger/critical phases for audio cues.
@@ -30,6 +34,8 @@ public class NukeBall : BallBase
 
     private float bounceDuration = 1.00f;
 
+    private bool exploding = false;
+
     // Start is called once before the first execution of Update after the MonoBehaviour is created
     void Start()
     {
@@ -55,6 +61,11 @@ public class NukeBall : BallBase
     // Update is called once per frame
     void FixedUpdate()
     {
+        if (exploding)
+        {
+            return;
+        }
+
         AnimatorStateInfo stateInfo = animator.GetCurrentAnimatorStateInfo(0);
 
         if (stateInfo.IsName("NuclearBallBounce")) {
@@ -100,14 +111,20 @@ public class NukeBall : BallBase
     {
         // Set critical state.
         var area = worldFiller != null ? worldFiller.GetAreaPercentOfFreeRegion(transform.position) : -1.0f;
-        criticalState = (area < 0.2f) ? 2 : (area < 0.4f) ? 1 : 0;
+
+        if (area == -1.0f || exploding)
+        {
+            return;
+        }
+
+        criticalState = (area < 0.12f) ? 3 : (area < 0.2f) ? 2 : (area < 0.4f) ? 1 : 0;
 
         // State 1 beeps every 0.5s, state 2 beeps every 0.25s.
         criticalTime = (criticalState == 2) ? 0.5f : 1.0f;
 
         // If in a critical state, increment the critical timer and play the
         // critical sound if the timer exceeds the critical time.
-        if (criticalState >= 1)
+        if (criticalState == 1 || criticalState == 2)
         {
             criticalTimer += Time.deltaTime;
 
@@ -119,6 +136,28 @@ public class NukeBall : BallBase
                 criticalTimer -= criticalTime;
             }
         }
+        else if (criticalState == 3)
+        {
+            audioSource.PlayOneShot(explosionSound);
+
+            var balls = worldFiller != null ? 
+                worldFiller.GetBallsInSameFreeRegion(transform.position) :
+                new Queue<GameObject>();
+
+            foreach (var ball in balls)
+            {
+                ball.GetComponent<BallBase>()?.StopBall();
+
+                if (explosionEffectPrefab != null)
+                {
+                    Instantiate(explosionEffectPrefab, ball.transform.position, Quaternion.identity);
+                }
+            }
+
+            exploding = true;
+
+            StartCoroutine(DestroyAndFillRegion(balls));
+        }
         else
         {
             criticalTimer = 0.0f;
@@ -198,4 +237,25 @@ public class NukeBall : BallBase
             }
         }
     }
+
+    private IEnumerator DestroyAndFillRegion(Queue<GameObject> balls)
+    {
+        yield return new WaitForSeconds(1.4f);
+
+        foreach (var ball in balls)
+        {
+            Destroy(ball);
+        }
+
+        var freeRegion = worldFiller != null ? 
+            worldFiller.GetFreeRegionOfPosition(transform.position) :
+            null;
+
+        if (freeRegion != null)
+        {
+            worldFiller.FillFreeRegion(freeRegion.Value);
+        }
+
+        Destroy(gameObject);
+    }
 }