Like Charlotte, I visited Candy's to buy a mask for the Elite Masquerade event*. The store has an amazing selection for costumes and all of the related accessories.
I perused the store to notice their assortment of costume makeup (Ben Nye theatrical makeup, Cryolan, clown paint, etc.), as well as the creepier aspects of costumes like fake blood, vampire teeth and zombie contact lenses.
The staff was very helpful despite being inundated with teenaged shoppers hunting for Halloween costumes. I purchased a plain glittery cat eye masque and embellished it on my own with pearls and ribbon from the local craft store.
All in all, Candy's is easily one of the best places in Toronto to get all your costume needs.
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* And just like her, I consulted the comprehensive product listing on their website prior to making the trip there.