Large costume and decoration store operated all year long located in South Etobicoke (right below the Gardiner Highway). There's a giant purple inflatable gorilla on top of the store to help you find this place as it is quite hidden. Their peak busy time is of course before Halloween and International BDSM Bondage Day (It's real, go look it up) for those folks looking for costumes.
The store is nothing spectacular but has all the essentials of what you would be looking for with respect to basic Halloween choices. Staff members are primarily jaded high school kids and there's even a giant entrance tent outside during Halloween for bag check, where they will hold on to your bag and provide you with a ticket stub as you cannot bring your bag into the store to prevent theft of silly foam and Bill Cosby masks.
Keep in mind, parking will be really hectic as you enter this place during Halloween season. Also be prepared for heavy in store traffic filled with people shopping around for Halloween ideas and thinking out loud, for example: " I think it would be sooooo hot, to dress up in cat ears for the 5th time in a row, but this year I will be a sexy cat with cocaine rage like a zombie. I wonder if they have white powder to put below my nose?"