Улучшил баланс. Корова идет к одному из ближайщих 3х растений. Учитывается так же размер растения. Если последняя корова умирает, то новая случайным образом спавнится.

main.py

@@ -19,6 +19,8 @@ class Cow(arcade.SpriteCircle):
     self.age_to_bride = 3
     self.health = 30
     self.speed = 5
+    self.move_target = 0
+    self.target_timer = 0
     Cow.ls.append(self)
   @classmethod
   def update(cls):
@@ -26,6 +28,8 @@ class Cow(arcade.SpriteCircle):
       c.age += 1
       if c.age >= 30:
         cls.ls.remove(c)
+        if len(cls.ls) == 0:
+          Cow()
         continue
       hit_plant = arcade.check_for_collision_with_list(c,Plant.ls)
       for p in hit_plant:
@@ -35,10 +39,12 @@ class Cow(arcade.SpriteCircle):
           c.health -= 30
         Plant.ls.remove(p)
       else:
-        near_plant = Plant.get_near(c.center_x,c.center_y)
-        if near_plant:
-          vec = cls.get_vector(c.center_x,near_plant.center_x,
-                             c.center_y,near_plant.center_y)
+        if c.target_timer <= 0:
+          c.move_target = Plant.get_near(c.center_x,c.center_y)
+          c.target_timer = 5
+        if c.move_target:
+          vec = cls.get_vector(c.center_x,c.move_target.center_x,
+                             c.center_y,c.move_target.center_y)
           new_x = c.center_x + vec[0]*randint(0,c.speed)
           new_y = c.center_y + vec[1]*randint(0,c.speed)
           if 0 < new_x < SCREEN_SIZE[0] and 0 < new_y < SCREEN_SIZE[1]:
@@ -79,14 +85,11 @@ class Plant(arcade.SpriteCircle):
       Plant.ls.append(self)
   @classmethod
   def get_near(cls,x,y):
-    min_dist = SCREEN_SIZE[0]
-    near_plant = None
+    dist_list = list()
     for p in cls.ls:
-      dist = ((p.center_x - x)**2 + (p.center_y - y)**2)**0.5
-      if dist < min_dist:
-        near_plant = p
-        min_dist = dist
-    return near_plant
+      dist_list.append((p,((p.center_x - x)**2 + (p.center_y - y)**2)**0.5 - p.width ))
+    dist_list.sort(key=lambda x: x[1])
+    return dist_list[randint(0,3)][0]
   @classmethod
   def update(cls):
     for p in cls.ls:
@@ -121,6 +124,7 @@ class MainView(arcade.View):
   def on_update(self, delta_time):
     self.cur_time += delta_time
     if self.cur_time >= TICK_TIME:
+      print(f'Total plants: {len(Plant.ls)}, total cows: {len(Cow.ls)}')
       Plant.update()
       Cow.update()
       self.time += 1