How about a (shiny?) Vulpix nicknamed "Trickster" with the egg moves Overheat, Power Swap, Hypnosis, and Disable (OR Role Play if you have access to it, but that's a HGSS tutor move, so you'd need access to breeding in HGSS... so likely not Role Play, but I'll leave this up to you of course ^.^)
Power Swap + Overheat could be a nasty surprise (forcing switches by giving any special sweepers your negative buffs in special attack caused by Overheat, while allowing you to keep firing them off at full power), but it sorta relies on the surprise factor to work properly. Not a standard set at all but might be worth some luls. XD
If you have access to Role Play, it fits in to the trickster fox mythology of it taking on different forms as a disguise. It could be funny to surprise a Jellicent/Vaporeon trying to hit you with a water move by copying their Water Absorb ability. It could also be amusing to start levitating when a Flygon attempts to Earthquake you. This is completely situational but this Trickster is all about the element of surprise, and being unique.
Hypnosis and Disable are fun annoying moves that could mess with your opponent, and they can help you stay around longer to throw more Overheats their way. Either could be replaced by a TM of choice or level up move, depending on what sort of Ninetales you want (energy ball/solar beam/will-o-wisp/etc). It's possible to get all of these egg moves using Smeargle. If you want a hidden power type, Ground might be an option to deal with Heatran or other Flash Fire 'mon.
With Role Play it would have to have the regular ability, without Role Play it can have the Drought dream world ability. :3