|It has been suggested that this article be renamed to C (anime). (discuss)|
The reason given was: per CXyz
"Chaos" monsters are all Xyz Summoned by Chaos Xyz Evolution - whether naturally or by a "Rank-Up-Magic" card - by evolving a specific Xyz Monster. When compared to these base counterparts, each of the "Chaos" monsters can be Xyz Summoned normally using 1 more Xyz Material that their original counterpart, but they must be of the corresponding Attribute (for the naturally-evolving "Number Cs") or 1 Rank higher (for the remaining "Number Cs" and all of the "CXyzs") than their base form.
In the background of Rank-Up "Chaos" monster, they all have a large vortex.
The two sub-categories of "Chaos" monster all share a common weakness with others in their group. For monsters Summoned by a natural Chaos Xyz Evolution, their effects cannot be activated while the controller's Life Points are above 1000. Monsters Summoned by the Rank-Up-Magic Spell Cards, however, have two parts to their effects, the second half of which becomes unusable while that monster's specific base counterpart is not attached to it as Xyz Material.