You can test if the boss is destroyed with the ‘get all actors of a class’ node that you connect with an event tick: if the length of the result array is equal to 0, you call the event witch spawn your enemies. But you have to test if you have spawned the boss with a bool variable that you set true after the spawn actor node. So you have to add a branch between the event tick and the get all actors node. At last you have to set the bool variable to false after the call of the spawn of the enemies event.