I've been coming up with a little theory about Paramecia DFs that I'd like to run by all of you.
It seems to me that there is a certain level of proficiency required to fully utilize the power of a Paramecia DF. With a few exceptions, we have seen basically two types of Paramecia abilities:
1. User Centered: The DF changes the properties of the user's body, but the user is not (yet) capable of changing the properties of any other target. Examples include Buggy, Mr. 1, Bon-chan, Jozu, and Baby 5.
2. Target Centered: The DF gives the user the ability to change the properties of one or more targets or to produce a substance from thin air (which could be seen as changing the properties of the air/space around them), but has no direct effect (yet) on the user's body. Examples include Hancock, Mr. 3, Foxy, Law, and Jora. It is interesting to note that these users are able to alter the properties of any target, living or inanimate. Even logia users have not yet been shown capable of literally turning another living person into their respective element.
However, I believe that the exceptions to the above rules are the most interesting. There are some Paramecia users who appear to have both of the above abilities at once. These include Wapol, Moria, Absalom, Capone, Ivankov, Inazuma, and others (there really have been a lot of Paramecia users in this story).
My theory is that, with a certain level of experience/aptitude, a Paramecia user can learn to use both of the above abilities. I would argue that Luffy is starting to cross this threshold (perhaps even started to cross it a long time ago). If the wacky way that Oda draws damage to Luffy's opponents (and then magically healing most of the way later) and Chinjao's newly sharpened skull isn't all just some running gag, then perhaps Luffy has already started to learn how to make external targets rubbery.
It's just an idea that I had, I don't even know if it's all that original. What do you all think?