Running too many loops and not keeping scope as narrow as possible can result in strain on the engine if you have too many objects at once, but everything in this gif is running using fast loops. From the player to the enemies, and every bullet and the particle effect generators and even the destructible terrain, and it stays at 60 fps (the gif is recorded at 33fps). (ignore the attachment, it's a jpeg, lol)
Til The End Stress Test
Oh, and the yellow enemies are all using dynamic pathfinding and line of sight detection as well.