Put this in your enemy script
visible = false
visible = true
Put this in your existing function
That assumes Enemy1sprint is a child of the node where this script is running. If that is not true you need to change the NodePath in get_node to the correct path.
But remember you want to do this for all the Enemy
One option is put them all in a Group, then call a hide function on every Enemy.
Details of Groups here
Or, probably better you can use a signal for this. You could create a "level_completed" signal. The Main script could react to that by changing the level, and each Enemy could react to that by hiding for 2 seconds. You can watch a good tutorial about signals here