Morphing into its Primordial form had reduced the Daggertail's mobility substantially, but this evolved form granted it even more powerful abilities.
It no longer needed to flicker into the shadows to avoid its pursuers. Instead, it could use its Shadow Clone ability to create a perfect replica and teleport to a safe location while its enemies were chasing the illusion.
With the Nightmare Gate empowering the Ethereal and the dark blanket of clouds covering the night sky, it was almost impossible to tell the difference between the actual Daggertail and its illusory form.
The only way to dispel the shadow clone was to inflict damage on the real Daggertail or play a card that could grant true sight. But Xander had already used his detection card while fighting the last Gadacro, leaving him with little options against the Primal Daggertail.