I like the idea of using an array, but I've never used them before, so bare with me.
Here is what I did (and maybe you can tell me what I'm doing wrong):
When an enemy is killed, I'm using the following event:
Enemies > On Destroyed
_____________-Array > Set Value at Enemies.ID(instanced variable) to 1
On the save button, I'm using:
Webstorage > Set Local Key "Array" to Array.AsJSON
Array > Load > JSON string "Array"
When the layout start, I created a subevent:
Array > Value of Enemies.ID = 1
For Each Enemies
____________- Destroy Enemies
The other thing is that I want all enemies to respawn when you leave the level and go back into the level, so I added a "Array > Clear" event for that, but it doesn't seem to be working either.