Smeargle can do anything.
So, I had an idea for a new Smeargle variant. It's completely conceptual but I'd like some other opinions on it. Feels slightly gimmicky and situational but highly unpredictable. I could be beating around the bush and this may turn out to be useless, but it's always worth a shot. Better to try than never try. Most people would expect to be slept, then set up upon. Or for Smeargle to wait for a good chance to endeavor.
This Smeargle's Job is to basically: Put a pokemon to Sleep, then, on the switch ( or not), swap Smeargle's terrible Attack/Special Attack with the incoming or currently present pokemon, or their Defense/Special Defense in the same fashion. This using, Spore, Power Swap, and Guard Swap. The point to try is to attempt to bring in Smeargle on slow walls, such as Cresselia.

Jolly- Own Tempo
252 HP/252 Speed
31/ < 10/<10/<10/<10/31
Okay, I know there is 4 Evs left, but if you add it, it would give the pokemon getting their Atk/SpAtk- Def/SpDef swapped an extra point higher. So, we just leave it. The lower the offensive and defensive IVs the better. Less than 10 really works out well here.
Spore
Power Swap
Guard Swap
ExtremeSpeed
After swapping Attack power all manner of things can still be faster than Smeargle, with it's mere base 75 Speed and a Max of 273 Speed. So of course, ExtremeSpeed, being a +1 Priority Move and having STAB for Smeargle will work great after power swap. Of course, because it's ExtremeSpeed and it's Physical, this wont quite work on walls and other pokemon with the lower side of attacking. The only problem is: it only works once, most of the time. You could steal the defenses of a Cresselia or Dusknoir, and then steal the attacking power of a TTar and then there's not much more to do, except you've just turned a perfectly good wall and a perfectly good sweeper into pudding. Snack time?
Other options here are Trick instead of Spore. You could have Smeargle with Choice Specs/Band and cause their pokemon to have to switch out, and Swap the incoming pokemon. Trick is even MORE gimmicky than the one with just spore. It's also less prone to actually working, considering how many sweepers have Choice items in the first place. If you just want a variant that can go in, Swap their defenses/offense and get out, Explosion is a great option over ExtremeSpeed. Just incase you get the "It's useless unless I kill SOMETHING" kind of mentality. Because ExtemeSpeed isnt always assured to allow you to kill after you do the swap.
Any steel or rock type really counters this, though the minimum defenses of 106/126 are really a problem for anything. Double Hit Ambipom also is a huge problem because it's both faster than Smeargle and will break his Focus Sash and KO. Taunt makes this useless. Ghost types wall this to an extent, meaning you can't attack but, you can cripple them, none the less. Residual Damage and Status will also ruin this particular Smeargle's day. With SR/Spikes/TSpikes up smeargle is unable to come in and still retain his sash. Burn makes Power Swap become useless on Smeargle's side. Paralysis turns Smeargle into a coin, Heads he goes, tails he fails. Could make the difference in surviving to Swap and Sweep or dying in misery.
Weather and Priority moves are really Smeargle's two biggest problems, as with any pokemon with Sash. Weather causes Smeargle to become unable to survive after sash is down. Priority moves cause a plethora of problems. First, they easily break down sash and drop to 1hp. Also, fast users of priority moves can outspeed Smeargle's ExtremeSpeed and OHKO , if sash is gone already, or 2HKO if not.
Overview: Since this Smeargle is able to entirely remove Blissey, Skarmory, Bronzong, Cresselia, Hippowdon ( Though forfeiting Sash), Spiritomb, Milotic, and other slow walls from being a wall at all. Or strong sweepers such as Salamence, Ttar, Weavile(Though sash will be gone, most likely), Infernape(" "), Heracross, from being a threat. This set can easily be used to determine if a game is won or lost. Though several counters exist, you could easily create a team that ensures atleast one wall or sweeper is completely nullified. Though, each swap only works once, it usually only has to work once for your opponent's team to fall apart.