Here's the list of the exclusive mask and their picture, almost all of them are listed under the "Event" tab in your mask stash and the icon won't appear until you have them.

In this section I'll explain briefly about methods of obtaining exclusive masks

Easiest method, but require the most luck in term of timing. Forums, reddit, and discord sometimes will have code drops, but you will have to race with others to get it, a tips to win the race is to always open steam code activation windows every time you want to browse forums/discord. Certain codes like Lootbag / Bobblehead / Alienware Alpha doesn't drop very often. Also please for the love of Bain don't beg for code drops in the forum :/.

NOTE: The following section is only for official contest held by moderators/developers
Another cheap method, require no luck, but time consuming and require high level of skill and dedication. Contest rarely appear in the forum with various prizes, and every so often the prizes is one of the exclusive masks. Based on my experiences, here's how mask codes usually given in contest:

• Winner: Lootbag / Bobblehead / Alienware Alpha(or all of them)
  
• Runner ups: Lootbag / Bobblehead / Alienware Alpha(choose one)
  
• Finalists: Humble Bundle Mask Packs / E3 Mask packs(Joker/King/Queen/Jack) / PAYDAYCON 2015
  
• Participant: Store DLCs

Most expensive method, require a bit of luck for high demand masks and extra cheap deals, but the most accessible method. Traders will usually prefer "Keys" as in CS GO crate Keys/PAYDAY 2 Drills, for high end masks, but some trader also accept skins or other items. Price can be varied from cheap to super expensive depending on the pack. Here's the list of estimated prices based on my experiences (in keys):

• Completely Overkill Pack (COP): 145-150 keys.
  
• Alienware Alpha: 50-100 keys
  
• Lootbag DLC: 30-60 keys
  
• Bobblehead DLC: 20-25 keys
  
• PAYDAYCON 2015 Mask pack: 2-4 keys
  
• Joker/King/Queen/Jack packs: 1-3 keys
  
• Humble Bundle packs: 1-3 keys
  
• Mega Clover and Sydney: 0-1 key (They drop very often I don't recommend to trade them)
  
• Party Hat: 0 key
  
  NOTE: Trading tips: It is very important to have mutual trust in trading codes due to how steam trading works. Try to find a known trader for trading codes or ask somoene trustable to be a middleman. Also please don't lowball and scam people. Also there is no Completely Overkill Pack (COP) codes, so beware.

Sometimes someone will brighten your days with a mask code in your chatbox (COP is a DLC so it's a DLC gift in that regard). This method is applicable to all exclusive mask.

Also applicable to all exclusive masks, almost identical to code drops, but instead of racing with others you will need to beat them in term of luck (Pray to RNG :p)/any method that the host preferred.

https://store.overkillsoftware.com/toys-collectibles/28/payday-2-figure-dozer-bobblehead?c=115

Due to high shipping cost in some country, sometimes it's more profitable to buy it via trading.

http://www.overkillsoftware.com/housewarmingkeys/

Just sign in via Steam and enjoy your party hat code.

Thank you for reading this guide, hope you'll get the exclusive mask you want! ^^

• FBI Files for the mask picture
  
• Overkill's sketchfab account for Party Hat icon
  
• PAYDAY 2 Trader and Collector's group for helping me estimating prices.
  
• PAYDAY 2 Achievement icons for obtaining method pic
  
• Overkill store's bobblehead dozer for obtaining method pic
  
• Naifrus for Party Hat suggestion.
  
• Lammah for Alienware Alpha price correction