Crab Soldier costume question
Since a Crab Spider's extra arms are essentially hardwired into their nervous system, they will appear on all of your costumes whether you want them to or not, so you should be able to get the look you want on any of your extra costume slots.
Currently published Mission Architect arcs:
Arc ID# 70466: From the Abyss.
Arc ID# 403174: The Serpent's Revenge.
Arc ID# 534236: The Clockwork Angel.
The first slot is limited to the Arachnos armour, and the limited varients there-of (usually one of two options, and a default/custom colouring for each)
going through your ongoing VEAT mission arcs, you get to unlock your first extra costume slot earlier than lvl 20 (or by turning in halloween salvage, whichever you do first). THAT slot, and all others after it, are more fully customizable (monstrous legs, robotic arms, etc, etc), with the exception that if you have any Crab spider powers; the spider-leg backpack is a mandatory back option.
EDIT: although I wish some of those costume pieces from slot 1 were options for the other slots. I <3 those crab spider glove blades.
"My inner mind has become a reality-cracking overgod. He torments me! Help!"
Ah! So it sticks the pack on everything! Awesome, thanks. =D
It even persists if you use a respec or the dual builds option to pick the Bane path instead.
Once you Crab Pack, you never go back.

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Really? Nice. Last I heard, even that wouldn't do it. Thanks for the info, Agg!!

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As I understand it, the backpack can only be displayed on the first slot. But the first slot forces you to kind of stick to a few options. Am I going to be able to, for example, give my crab the robot/tech monstrous legs in his first slot, to go with the backpack? Or am I stuck with the "arachnos armor" legs and look in that slot?