Well really all this is a guide for my friends, but I guess I'll share it with everyone. This contains links, tips, and all that fun stuff for making a nice cosplay. (today I will only be focusing on Vriska, if toi would like another, just ask)
VRISKA

I have helped a friend do this cosplay, so I know what to do about this. The plus complicated stuff will be listed first, also, keep in mind this is not god tier vriska.
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One of the most challenging things about this cosplay is the arm. My friend and I used a simple method using craft foam. Here’s some useful tutorials:
link
. This one involves a cloth version of the arm.
.Requires patience and good art skills(or at least moderate skills)

link
-A plus complicated GREAT one
-We used something similar to this method. It turns out great.
O-Materials are listed in the links-O


Possible wigs:
link
link
link

-Vriska's hair is lengthy and slightly curly. Use a reference if toi will when styling a plain black wig.

Shoes(easy one):
link that’s the cheapest
link seconde resort

-Really all ya need are red converse. LOW TOPS.

Makeup: Really,all toi need to do is buy blue lipstick, Ben Nye grey body and face make up, and blue eyeliner/eyelashes.

Shirt: If ya want a legit one, visit the sites listed on the mspa homepage.
If ya don’t, buy some iron on wax, a black t-shirt and use this template:
link

As for her other clothes, I would use clothes like these:
link
-Or just go to your favori shopping outlet, and look for a long sleeve grey button up shirt, a long sleeve jacket, and blue jeans. For the glasses, just wear sunglasses and pop out one of the lenses.

-For the horns,you may buy them online. I know of some people who are currently selling horns at good prices. (I will liste them below) But,of course toi may make your own. If toi do,I'd advise using:
-MM clay CRAYOLA BRAND (model magic)
-Acrylic paints (Dark orange,lighter orange[close to yellow], and yellow. If toi are on a tight budget, get yellow and red, then mix them to your liking)
- Styrofoam
-gloss
For help, Here's some tutorials:
link

Where to buy horns:
link

Cosplay and horn references:
link
link
link

BLOG THAT WILL HELP toi WITH ANY Homestuck COSPLAY:
link