Question

Really it should have been just Sand Veil is banned on Garchomp, as it is not OP on any other Pokemon.

Answer 1

It is banned in general

On October 15th 2012, Sand Veil was voted to be banned from Smogon's OU metagame as well as all tiers below it, so is currently unusable in all Smogon metagames bar Ubers.

Source

Comments

LAME. We have a Swift Swim ban specific to Drizzle. I call this weather discrimination.
And as a general rule this is logically and competitively flawed.

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SS is banned with Drizzle because most SS abusers gain STAB from Water type attacks, meaning they get boosted speed and STABs, but I agree that SV should only be banned w/Sand Stream.