So lets say in a double battle scizor uses swords dance then weezing uses haze, then another Pokemon uses defog. Will the stat changes be back?
No.It will only eliminate the effects of Light Screen, Reflect, Mist, Safeguard, Spikes, Stealth Rock and Toxic Spikes on the oppenent's side of the field.
Defog, despite the name, does not get rid of Haze. Defog would lower the accuracy of all Poke'mon but the user.
No. Haze already cancelled out the stat changes, and there is no way to recover stat boosts / drops without redoing them.
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