Does equipping or obtaining bone charms void "Mostly Flesh and Steel"?
Mostly Flesh and Steel
Finish the game without purchasing any supernatural powers or enhancements, besides Blink
Does obtaining or equipping one of the bone charms you can find throughout the game void this achievement?
No, this achievement refers only to powers, not bone charms.
Note that or enhancements in this case refers to the Blink Level 2 upgrade.
Do not purchase any new powers, and do not upgrade Blink.
Bone charms are safe.