To get this you have to collect all the costumes listed in the Collectible menu in the game. There are 87 total items to collect.
I'm going to break this solution up into 2 sections: Missable and the full list. I'll list the missable ones in the order that you'll find them, and then the full list in the order they are in the collectibles menu. This is a prerequisite trophy for
Missable Costumes - you only get one shot at these.
*** Spoiler - click to reveal ***Giggling Donkey
* Wood Elf Gloves - After defeating the the elves in the attic, this can be looted off of one of the bodies. It is possible to avoid them, so don't. They have to be defeated before leaving Jimmy's house; however, the loot can be picked up the following day (Jimmy's house is locked after you beat the game, so get this before then).
* Wood Elf Cap - It's in the yellow chest on the right side of Jimmy's Room. You can go back into Jimmy's house anytime before you beat the game and get this out of the chest, but once the game is beaten, Jimmy's house gets locked up.
Alien Spaceship
* Alien Helmet - After escaping from the probing machine, it is in the purple chest behind Randy.
* Alien Suit - After taking the first elevator down, It is in the purple chest to the left.
* Alien Gloves - In the red room next to the first elevator, this can be looted off of the defeated Alien Space Officer.
* Tinfoil Hat - When coming back up the first elevator after lowering the force fields, the floor in front of the probe room will have an opening you can go down. Defeat the Hobo that is hiding in the pile of garbage in the right side of the room, and loot his body for this.
"Taco Bell" Construction Site
* SWAT Vest - After entering through the vent and defeating the Nazi Zombie, loot the SWAT agent body on the right side of the entry way to get this.
* SWAT Tactical Gloves - After entering through the vent and defeating the Nazi Zombie, loot the SWAT agent body on the left side of the entry way to get this.
* SWAT Armored Headgear - After entering through the vent and defeating the Nazi Zombie, loot the SWAT agent body on the left side of the entry way to get this.
The School (2nd time)
* Necromancer Gloves - After defeating the enemies on the other side of the barricade in the left side of the Cafeteria, you can loot this off of one of their bodies.
* Necromancer Robes - This is on one of the Gingers in the basement of the school in front of the Boiler Room after the puddle of water.
* Necromancer Hood - As soon as you enter the second floor of the school, defeat the 3 enemies attacking your fellow elf/human. Loot this off one of them.
Gnomes
* Gnome Gloves - After defeating the Gnomes that wake you up and shrink you, loot their bodies for this.
* Gnome Helmet - After entering the Gnome hole in your room, climb the first set of wires. This is in the yellow gnome pouch to your right.
* Gnome Clothes - After exiting the vent that looks into your parents' room, climb the wires, and break the chunk of wall to the left. This is in the yellow gnome pouch to the left all the way at the end.
* Underpants "Helmet" - After defeating the Gnomes on the dresser in your parents' room, loot their bodies for this.
Clyde's Fortress
* Knight Gauntlets - After entering the fort, you can loot this off the body of one of the firework launchers on the upper level of the first room after they are defeated.
* Knight Helmet - This is in a yellow chest in the tower to the right of Ike.
* Knight Armor - In the room where you defeat Craig, this is in the yellow chest on the left side of the upper level (where Stan comes in).
Inside Mr. Slave
* Condom Cap - Turning on the flashlight, that you get to, reveals a yellow chest. This is inside that chest.
Costumes List - here's where to find them in order of the menu.
1.
Crown of Anal Pleasure - This is automatically obtained after completing the Mr. Slave Main Story line quest.
2.
Barbarian Costume 3/3 - These 3 are found separately in Canada:
*** Spoiler - click to reveal **** Barbarian Gloves - Part of the "Big Game Huntin' With Jimbo" side quest (started by buying the Hunter's Guide to South Park Wildlife Book from the Miscellaneous section in Jimbo's Guns shop). One of the tasks is to kill the Canadian Barking Spider. Once you get access to Canada late in the game, go to the Northeast corner where a square spiderweb is. Set the bait of Poutine on the web and the fight will the spider will begin. Defeat it, and the Gloves are automatically obtained.
* Barbarian Helmet - In the Duke of Vancouver's bedroom (on the left side of the north house in Vancouver, Canada), is a breakable wall to the north. Break through the wall, and this is inside the blue chest on the other side.
* Barbarian Armor - Inside the cave north of Ottawa, Canada, Nagasaki is required for this. After getting the Nagasaki fart ability, enter the cave and destroy the boulder with this power. There is a treasure chest to the left behind the group of dire animals. After defeating them, the armor is inside the chest.
3.
Minstrel's Costume 3/3 - These 3 are all purchased from the Elvenwares shop in the Elven Kingdom for a total of $35.00.
4.
Wife Beater - This is inside Kenny's garage. There is a yellow chest in the center of the room behind the propane tank that is fueling the burner. Navigate around from the refrigerator to reach this chest.
5.
Leather Costume 3/3 - These 3 are all purchased from the Sparkle Boutique shop in the Girls Hideout for a total of $45.00.
6.
Bling - Inside the police station evidence room (up the stairs to the right). Move the ladder over by pressing the red button in the center of the wall, and climb the ladder to the yellow chest on the top shelf. It's inside the chest.
7.
Training Gloves - Purchased for $2.00 from the Street Merchant store outside of U-Stor-It.
8.
Cheese Costume 3/3 - These 3 are all purchased from the PTA Store shop (Mr. Mackey) in the Community Center for a total of $35.00.
9.
Condom Cap - MISSABLE - see Inside Mr. Slave in the Missables above.
10.
Crab Costume 3/3 - The
Crab Pincers,
Crab Helmet, and
Crab Carapace are in the yellow chest to the left of the Crab Person in the sewers. Directions:
*** Spoiler - click to reveal ***The chest is located inside the back entrance to the sewers. It requires the Alien Probe and the Nagasaki fart ability to reach it; both of which you get playing through the story. Once you get the Nagasaki fart ability in Canada, you get to the chest via:
1. If you've already unlocked the back entrance to the sewer (to the left of the Movie Theater), then go down the manhole ladder and head to the left. You will see a boulder with green veins. Use Nagasaki to destroy to boulder, and go left on the path that is now open to the chest.
2. If you haven't unlocked the back entrance to the sewers yet, go to the sewers through the main sewer entrance in downtown. Use the Alien Probe Teleporter to cross to the other side and head down the ladder. Shoot the red wheel on the pipe to allow you past the sewage, then u-turn around the wall at the generator. Go left. When you get to a ladder go up, and at the top of the ladder go right behind the wall. Keep going right until you get to another pipe to shoot, then go down the first ladder and head right. Turn the gold wheel to lower the water, then come forward and go right. Shoot down the ladder at the top of the screen and go up. Go left and then trough the tunnel. Here, flip the switch, go right, break the pallet, go down the ladder, and then through the tunnel (before the gate closes back down). Shoot the pipe, then head right and take the ladder down. Head left (feel free to use the switch to slide the bridge to the left out - in case you need to get through here again) and then go through the tunnel in the back of the room. Head left, turn the gold wheel, and go through the tunnel with the red light above it. Go down the ladder, and walk to the right until you see a boulder with green veins. Use Nagasaki to destroy to boulder, and go left on the path that is now open to the chest.
11.
Surgical Costume 3/3 - The
Surgical Scrubs,
Surgical Cap, and
Surgical Gloves are automatically obtained during the "Unplanned Parenthood" visit as part of the quest. You'll pick them up in the Operating Room A after the doctor sees you, as you need to equip them to get access to the Records Room.
12.
Druid Costume 3/3 - These 3 are found separately in South Park garages:
*** Spoiler - click to reveal **** Druid Gloves - It's inside the yellow chest above Butters' Garage (the key found in his parents room in the nightstand to the right). Use the ladder to reveal the chest.
* Druid Crown - It's in the yellow chest above Clyde's Garage to the left of Pete Melman. Shoot down the ladder, then head up to reveal Pete and the chest.
* Druid Robes - It's in the yellow chest above Stan's Garage. Use the ladder to reveal the chest.
13.
Du Rag - Purchased for $2.00 from the Street Merchant store outside of U-Stor-It.
14.
Wood Elf Costume 3/3 - 2 MISSABLE - These 3 are found inside the Giggling Donkey (Jimmy's House) after you gain access in the story.
*** Spoiler - click to reveal **** Wood Elf Gloves - MISSABLE - see Giggling Donkey in the Missables above.
* Wood Elf Cap - MISSABLE - see Giggling Donkey in the Missables above.
* Wood Elf Armor - This is obtained automatically after defeating the group of 3 elves (with the one in the Bane Mask) in the living room (unavoidable) on your way to get upstairs.
15.
Friar Costume 3/3 - These 3 are found in chests at Token's House and Tweek's Bros. Coffee.
*** Spoiler - click to reveal **** Friar Cap - It's inside the top area of Token's Garage (get the Gas Mask from Jimbo's Guns to get past the Sercurity Guard). Use the ladder to reveal the chest.
* Friar Robes and Friar Gloves - They are both in the yellow chest in the back room of Tweek Bros. Coffee, up on a ledge behind the coffee machines.
16.
Gnome Costume 3/3 -MISSABLE - The
Gnome Gloves,
Gnome Helmet, and
Gnome Clothes are found during the Main Story quest (see Gnomes in the Missables above).
17.
Goth Costume 3/3 - These 3 are all purchased from the Street Merchant store in front of the U-Stor-It for a total of $16.00.
18.
Sweaty Headband - Purchased for $2.00 from the Street Merchant store outside of U-Stor-It.
19.
Clyde’s Helmet - Purchased from the Kupa Keep Armory for $6.00 after Clyde has been banished.
20.
Gas Mask - Purchased from Jimbo's Guns store for $5.00.
21.
Jester's Cap - It's in the yellow chest in Jimmy's Garage.
22.
Khan Costume 3/3 - These 3 are all purchased from the Kupa Keep Armory shop in the Kupa Keep Kingdom for a total of $45.00.
23.
Knight Costume 3/3 -MISSABLE - The
Knight Gauntlets,
Knight Helmet, and
Knight Armor are found during the Main Story quest (see Clyde's Fortress in the Missables above).
24.
KKK Costume 3/3 - These 3 are all purchased from the Kupa Keep Armory shop in the Kupa Keep Kingdom for a total of $35.00.
25.
Monk Costume 3/3 - These 3 are all purchased from the Elvenwares shop in the Elven Kingdom for a total of $40.00.
26.
Necromancer Costume 3/3 -MISSABLE - The
Necromancer Gloves,
Necromancer Hood, and
Necromancer Robes are found during the Main Story quest (see The School (2nd time) in the Missables above).
27.
Bishop Costume 3/3 - These 3 are all purchased from the Banff General Store shop in Banff, Canada for a total of $45.00 or $55.80 Canadian.
28.
Woodsman Costume 3/3 - These 3 are all purchased from the Elvenwares shop in the Elven Kingdom for a total of $40.00.
29.
Alien Costume 3/3 -MISSABLE - The
Alien Helmet,
Alien Suit, and
Alien Gloves are found during the Main Story quest (see Alien Spaceship in the Missables above).
30.
Fairy Princess Costume 3/3 - These 3 are all purchased from the Sparkle Boutique shop in the Girls Hideout for a total of $50.00.
31.
Squire Costume 3/3 - These 3 are found separately in South Park via the Alien Probe obtained after the first night:
*** Spoiler - click to reveal **** Squire Gloves - On top of the Bank in Downtown is an Alien Probe Teleporter. Teleporting to the roof reveals another Teleporter on top of Tom's Rhinoplasty. On this roof to the left is a yellow chest wherein the Gloves are located.
* Squire Helmet - This is on the roof of the back unit (#240) at the U-Stor-It. To get to it, get inside the U-Stor-It facility and walk to the back and right. In this back section, walk all the way to the right to the last unit. Inside here, walk around so you can go up the ladder in the back. Go into the duct work and up the ladder that is revealed. From here use the Alien Probe Teleporter on the Telephone pole to teleport over to the roof of Unit #240. It is inside the yellow chest.
* Squire Armor - This one is on the roof of Token's house. Go into the garage and up the ladder. Walk to the left side of the upper area over the garage and use the Alien Probe Teleporter to the left to get on the roof of the house. Walk over to the chimney to the left and break it. The Armor is inside the yellow chest that has been revealed.
32.
Stupid Spoiled Whore Costume 3/3 - These 3 are all purchased from the Sparkle Boutique shop in the Girls Hideout for a total of $40.00.
33.
SWAT Costume 3/3 -MISSABLE - The
SWAT Vest,
SWAT Tactical Gloves, and
SWAT Armored Headgear are found during the Main Story quest (see "Taco Bell" Construction Site in the Missables above).
34.
Tinfoil Hat - MISSABLE - see Alien Spaceship in the Missables above.
35.
Underpants “Helmet” - MISSABLE - see Gnomes in the Missables above.
36.
Valkyrie Costume 3/3 - The
Valkyrie Gloves,
Valkyrie Headband, and
Valkyrie Armor are all found in the yellow chest behind Jessie in the Girls Hideout (inside the girls bathroom at the basketball courts - unlocked as part of the story after you successfully help the girls out with their issue).
37.
Witch Costume 3/3 - These 3 are found separately in South Park via the Gnome Dust obtained after the second night:
*** Spoiler - click to reveal **** Witch Gloves - To the Left of Jimmy's House is a Gnome hole in the fence. Shrink down using the Gnome Dust and go through the hole. To the right is a yellow chest wherein the Gloves are located.
* Witch Hat - This is inside a yellow gnome pouch under the bench outside of Tweek Bros. Coffee. Shrink down and walk under the bench from the left side to the right to collect.
* Witch Robes - This is inside a yellow gnome pouch, that is inside a log with a hole in the end, on the other side of the path the Stark's Pond, to the left of the School. Shrink down and walk into the hole from the left side of the log to collect.