Is decoy an important spell to have?

[Puddnhead]

That was my point. If they use am arcane ward to try and clear off your arcane ward, and it was a decoy instead, then they have now protected your enchant from whatever they were trying to follow up their AW with.

Sort of.  On a mandatory reveal you are always allowed to choose not to pay the cost and discard the spell without effect.  So your opponent could choose not to pay the 0 mana and discard the ward in order to play a different spell on the non-mage object.

[Zuberi]

That was my point. If they use am arcane ward to try and clear off your arcane ward, and it was a decoy instead, then they have now protected your enchant from whatever they were trying to follow up their AW with.

Sort of.  On a mandatory reveal you are always allowed to choose not to pay the cost and discard the spell without effect.  So your opponent could choose not to pay the 0 mana and discard the ward in order to play a different spell on the non-mage object.

This is correct.

[RomeoXero]

That's true, but in that case they wasted half the arcane ward and shoulda used a decoy instead