Reallyl nice Extra! I do agree that the structure of the document is kind of messy, in particular the first parts, so I might missunderstand some stuff. My primary feedback is probably that the whole extra seems to mechanize stuff to a degree that clashes with Charge general feel. An example of this is the danger rating that goes from 0-4 instead of 1-3 that other systems use. And since the danger rating is mentioned to vary depending on attacking limb, maybe this should just be a Detail associated with each Limb? "Long muscular arms" gives worse position for anyone trying to get close. "Indestructible bone plating" reduces the effect for any physical damage against the core while the limb is active, and so on. I guess you could still kind of a "Average Danger Rating" or "Max Danger Rating x Limbs" score that is derived from the current narrative situation but I have a hard time seeing a value with it.
Similar with monster speed, it should probably be something that is granted by a Limb so that it is possible to affect by player actions. Maybe a part of the function of monster speed could be broken out into a Monster Tactic detail that kind of describes how much care they show for their own safety?
Suggestion: Instead of the Hoard rule maybe rather have some kind of cluster system that can function as a replacement to a Core. Attacking the Cluster might require extraordinary effects to even make a dent but if you successfully reduce the Cluster it means that you have split apart the Cluster and each Limb can be dealt with as a separate entity with it's own core and limbs if necessary (or maybe each limb just turns into a mook character that can be one-shotted. I just imaging trying to keep track of a 100 zombie hoard where each clock has to be maxed out to defeat it... having a zombie cluster with a clock that is very hard to tick would probably be much more manageable and conform to how most people think of things like a zombie hoard.