You don't just have to rely on your defenses, and it's probably best that you don't. You can also use your abilities to place drones and more on the field. The basic drones, Demon Goonies, are great for slowing down enemies, but their damage isn't great - though, you can upgrade them to explode on death, making them much more formidable. Your drones and abilities, such as Soul Impact, are perfect for getting a large crowd of enemies together, and then finishing them all off at once.