The formula for creating a mixolydian scale from scratch is this: whole, whole, half, whole, whole, half, whole, or 1, 1, 1/2, 1, 1, 1/2, 1, whichever you prefer. So, C (whole) D (whole) E (half) F (whole) G (whole) A (half) Bb (whole) C. There you go! C, D, E, F, G, A, Bb.
If you prefer to compare scales to ones you alread know, to generate the Mixolydian scale from a major scale, flatten the seventh (b7). So, C Major = C, D, E, F, G, A, B. B is the 7th, so flatten it to Bb to get C Mixolydian. Got it?
"You must stab him in the heart with the Bone Saber of Zumacalis... well, you could stab him in the head or the lungs, too... and the saber, it probably doesn't have to be bone, just anything sharp lying around the house... you could poke him with a pillow and kill him."
- Aqua Teen Hunger Force, The Universal Re-Monster