i. You can only put one of the opponent's Pokemon to sleep at any one time, so if you used Spore, your opponent will switch Pokemon and be able to attack you.
ii. Hypnosis has an accuracy of 55%, meaning it's liable to miss, so if your Smeargle is KO'd and the spored Pokemon wakes up, you'd be wasting your time if Hypnosis misses.
iii. You are 100% liable to Taunt and Encore. If you are taunted, then all you will have left is struggle & you will deal damage to yourself. If a Pokemon puts in a substitute, toxic is useless (and nearly everything will outspeed Shuckle). If you are encored, this set is useless. A lot of teams carry Prankster Pokemon like Liepard or Whimsicott, which will render your set useless.
iv. Neither Smeargle, Drifblim or Shuckle have a speed stat that's brilliant, although Drifblim does have Unburden as one of its abilities, it will only activate if its held item is consumed.
v. Smeargle is easily KO'd, even with focus sash. Many Pokemon carry priority moves like Bullet Punch/ Aqua Jet/ Mach Punch.
vi. If your opponent carries Haze then your Shuckle is doomed. Haze isn't actually that uncommon what with Cofagrigus being a popular wall.
vii. Any Steel type will be able to to wall you completely, being immune to toxic and unaffected by sandstorm. A Pokemon like Nidoking/ Nidoqueen will also be immune to the effects of those moves as well. Also, a Pokemon with Synchronise will affect your Shuckle with poisoning too, and if your opponent just keeps switching Pokemon, your Shuckle will wear itself out with its poisoning.
This is a really gimmicky strategy that requires so much set up and such specific circumstances that it's not worth using. At all.