The 'god beast' that attacked the Dominion of Man was by far the trickiest opponent she had fought against!
As everyone could figure out with ease, the dreadnought always fared better in direct combat. The Dominion of Man dominated the earlier waves with remarkable ease because she had no problem aiming her massive gun batteries and potent Rubicon at large but obvious targets.
The mirror beast broke that pattern.
Its domain directly prevented the dreadnought from detecting the location of its true body.
It also generated illusionary beings that had the annoying tendency of reflecting most attacks that struck their forms.
Even so, the Dominion of Man still shouldn't have struggled so much. Her sensor systems were state-of-the-art, and had been upgraded several times over due to all of the lightning baptisms they received.