Just had a stroke of inspiration, and checked something - Nincada can learn Mimic in gen 3. Therefore, doesn't that make it possible to have an Endeavour-Shedinja? Ie:
255 Att, 255 Speed (No point in adding to the other stats)
Here's basically how it would work. Bring in Shed on something that won't use an SE move at that point (eg Ursaring/Groudon's moves other than V-Create), and endeavour on the switch (or survive hit with Focus Sash, then attack). ES/SS for the priority kill (SS/Sucker Punch in turn are the only priority to hit Sheddy). The other moves are a matter of fancy - Protect/Detect simply because I had no idea what to put. Destiny bond could be an interesting one though - With a Focus Sash, you can survive a hit, and then Destiny Bond. The opponent probably won't like their sweeper from fainting so soon, so this will prompt a switch, allowing Endeavour-ing.
I think this guy could be the answer to combatting some of the top threats in this metagame. You can come in on most of the top threats if you predict they aren't going to use an SE move (Ursa's Fake out/ES, Groudon's EQ etc) and possibly get a KO out of this. This guy is NOT meant to be able to sweep - thought is rather silly actually - but he can be VERY useful.
I'm going to try him out myself as soon as I have the time.
Soul Silver Pokedex: 493 seen, 493 caught
Battle Factory record: 33 wins, 29 trades.
Battle Tower record: 42 consecutive wins with 12 attacking team of: Infernape, Latios and Metagross. If only I could get at least 7 more...