I attempted to play trough the demo without any artifact. Thanks to my browser slowing down the game, I was successful!
The fourth wave was a chore. Without any damage increase the 3 ogres survive until the 2 cyclops spawn and the faster cyclops get in front of the ogres, blocking your shots with their 40 health.
The Boss herself was easier than I thought. It feels like her strikes and thunderclap attack hitboxes extend a fair bit upwards but not very far down. The strikes can be dodged easily by walking down and towards her, and the thunderclap and lightning fan charge long enough for you to get out of the way.