Does he need to be able to throw/breathe lightning? Is there some sort of canon/Sue creature that can only be killed by lightning in the continua you'll be working in? Could the job be done without throwing lightning around and magically shapeshifting whenever your Agent feels like it?

... and apparently, center-clicking on the "return to messages" button (to bring it up in a new tab) posts the message. Good thing I finished the sentence...

Anyways, to continue with my thought, Acacia manages to carry enough stabby things to mangle a small army, regardless of disguise. Details change to fit the disguise - bows become big ugly Uruk-Hai ones, arrows become poisoned, and so on, but the weapons stay around, useable, and canonically correct. I would add a caveat to that, Continuums don't know what to do with anachronistic weapons, so a shotgun brought into Middle-Earth would remain a shotgun.

I would strongly advise against making an agent into a dragon, especially if it works perfectly and there are no humorous side effects afterwards. Look at what the PPC does: We're ordinary people slowly going insane because we're trying to do an impossible job to save not just one world, but many. Becoming a flying, hyper intelligent, armor plated, magic-wielding, fire-breathing killing machine really doesn't seem to me to fit that theme.

There have been crazy fanfiction ideas that have worked, and worked really well (E.G. "hey, let's make a school for suethors where all the Canons are teachers!"), but this one really does concern me. I'm not sure how practical, or even possible, it would be to pull off well.

Also, you must consider that a dragon is a fairly significant creature in a lot of continuums, to the point where a dragon agent could well be noticed and forced to play the part of a random dragon - which would be just as disruptive to the Council of Elrond as, say, a Sue. (And quite a bit more risky, too - Glorfindel took down a Balrog, I suspect he could do the same to a dragon.)