Added marixil's work, v1.1

Assets/Scripts/Arrows.cs

@@ -0,0 +1,33 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+public class Arrows : MonoBehaviour {
+	SpriteRenderer spriteRenderer;
+
+	void Awake() {
+		spriteRenderer = GetComponent<SpriteRenderer> ();
+
+		StartCoroutine (FadeCoroutine (0.01f));
+	}
+
+	IEnumerator FadeCoroutine(float period) {
+		float absolute = 1.0f;
+		float degree = -0.01f;
+
+		while(true) {
+			//wait
+			yield return new WaitForSeconds (period);
+
+			//fade routine
+			absolute += degree;
+
+			//fade
+			spriteRenderer.color = new Color (1, 1, 1, absolute);
+
+			if (absolute == 0f) {
+				Destroy (gameObject);
+			}
+		}
+	}
+}

Assets/Scripts/Arrows.cs.meta

@@ -0,0 +1,13 @@
+fileFormatVersion: 2
+guid: 8afcae652a543cc43b32dac1312803f4
+timeCreated: 1523573797
+licenseType: Free
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Scripts/GameController.cs

@@ -20,7 +20,7 @@ public class GameController : MonoBehaviour {
 			Application.Quit ();
 		}
 
-		if (PersistentData.timer <= 0 || Input.GetKeyDown("space")) {
+		if (PersistentData.timer <= 0) {
 			SceneManager.LoadScene ("gameover");
 		}
 

Assets/Scripts/GameOverController.cs

@@ -81,7 +81,7 @@ public class GameOverController : MonoBehaviour {
 		if (open == false) {
 			scoreText.text = "Player's Score:       " + PersistentData.score + "\n";
 			scoreText.text += "Camera Clicks:        " + PersistentData.clicks + "\n";
-			scoreText.text += "Monsters Captured: " + PersistentData.monsterNames.Count + "/4";
+			scoreText.text += "Monsters Captured: " + PersistentData.monsterNames.Count + "/8";
 		} else {
 			scoreText.enabled = false;
 			creditText.enabled = false;

Assets/Scripts/Monster.cs

@@ -13,9 +13,11 @@ public class Monster : MonoBehaviour {
 	}
 
 	Rigidbody2D rigidBody;
+	SpriteRenderer spriteRenderer;
 
 	void Awake() {
 		rigidBody = GetComponent<Rigidbody2D> ();
+		spriteRenderer = GetComponent<SpriteRenderer> ();
 	}
 
 	void OnMouseOver() {
@@ -36,6 +38,26 @@ public class Monster : MonoBehaviour {
 	IEnumerator DestroySelfAfter(float seconds) {
 		//clean up lost objects
 		yield return new WaitForSeconds (seconds);
-		Destroy (gameObject);
+		StartCoroutine (FadeCoroutine(0.01f));
+	}
+
+	IEnumerator FadeCoroutine(float period) {
+		float absolute = 1.0f;
+		float degree = -0.02f;
+
+		while(true) {
+			//wait
+			yield return new WaitForSeconds (period);
+
+			//fade routine
+			absolute += degree;
+
+			//fade
+			spriteRenderer.color = new Color (1, 1, 1, absolute);
+
+			if (absolute <= 0f) {
+				Destroy (gameObject);
+			}
+		}
 	}
 }