They are very different sounding, completely different type of headphones. You can't really A/B compare a closed back dynamic can and an opened back planar...
First of all Mojo is a brilliant device, but not really enough to drive the 2C adequately. You won't get the bass performance it is capable of from a full sized amp.
The X00 is a fun sounding headphone with elevated and punchy bass and elevated treble. Recessed mids and a very forward, almost aggressive sound and a slightly cramped soundstage. It easily strikes inexperienced ears as the more exciting sound at first.
The 2C is a more mature sound that needs proper amplification. It sounds airy, neutral, natural and balanced in comparison. Also relaxed compared to the X00. With proper amping and enough time to adjust to the sound you will discover that the bass is more accurate and better balanced. The mids come alive but the treble is bit rolled off. I couldn't listen to X00's sharp treble.
Ultimately it is personal taste, perhaps you are not at a point in your journey yet where you can fully appreciate an opened planar sound.
These two headphones however are very different too. The 2C is technically on a much higher level but you need an amp with it.
What amp do you recommend that I can pair with the Mojo that's under $300?