Vaporeon @ Damp Rock Evs: Sp.Def , Hp , Def Trait : Hydration - Rest - Acid Armor - Toxic - Rain Dance
Vaporeon uses Acid Armor first turn if the opponent is physical attacker, otherwise it uses Toxic. Then, use Rain Dance or Toxic (if you didn't use it first turn) and then uses Rest. Because of Hydration and Rain, sleep is cured and you are fully healed. Then you just continue to stall.
It would work, but this strategy has a number of things that wreck it.
Any poison or steel type. Aegislash and Mawile are quite common. If either of them or any other poison or steel type shows up you're screwed.
Substitute. Another common competitive move on stallers. You can't toxic if they are behind substitute.
Taunt. You can't do anything if they taunt and you are forced to switch out.
OHKO's. If they have enough attack and you cant get acid armor up you will get OHKO'd.
This strategy honestly can't be used competitively as it has too many flaws.