So I've been sort of mentally constructing a deck, but haven't put anything together, but let's go over the thought process and talk about the basic ideas that I have and see if we can't construct a starting point.
Starting point: Why
Volrath, the Shapestealer? What are we trying to make/accomplish?
He's neat and I want to use him. Not a deck that is just his colors; doing things with the commander is the goal. Opportunities with opponents creatures are great, and we'll want them, but those are outside of our direct control. If you want to have toys to play with, the best bet is to always bring your own. We'll want creatures that Volrath wants to Shapesteal, and the ability to do so. We'll also want ways to protect him and keep him on the battlefield. So there is the starting point.
So the thing that separates Volrath from being a typical clone, is that he becomes a 7/5 of whatever creature he copies. What are the ways in which that matters,
Quick Note: Infect is one obvious answer. I can definitely see building an infect deck out of Volrath, but that doesn't appeal, so none of that right now.
You have various saboteurs that give you effects based on how hard they hit:
Cold-Eyed Selkie
Needle Specter
Dreamstealer
Cephalid Constable
Some protection and neat abilities:
Aetherling
Thornling
Predator Ooze
Protean Hydra - It's not indestructible, but does make Volrath basically immune to damage
Master Biomancer (Double Duty - an awesome copy target as well as counters on your dudes)
Viridian Joiner
Tracker - might be too weak
Abyssal Hunter - also might be weak
Heroes' Bane -
Chameleon Colossus is a second option for this effect, but you have to copy a nonblack creature, THEN copy it to use it's ability.
Champion of Lambholt
Cards that make sure you have counters on your boys to copy (Our biomancer buddy is already covered):
Forgotten Ancient
Loyal Guardian
Hadana's Climb
Unspeakable Symbol
The Great Henge
So if that's the core of what we are doing, what's the decks strategy?
Play dudes. Buff dudes. Copy dudes. Smash in hard with both commander and dudes. It looks like we can make it so if our Commander hits in combat, we can obliterate our opponents hand or board, or simply make him monstrously huge. While not purely a voltron thing, we can also go pretty wide and have a lot of our creatures be rather large and smash that way.
So if that's the strategy, we build out from there with Support (ramp, and other supplemental effects), Protection, and Disruption.
Interesting Disruption for our opponents creatures that works with what we are doing:
Hapatra, Vizier of Poisons
Yawgmoth, Thran Physician
Necroskitter
Serrated Biskelion
Harbinger of Night
Protection that works well with what we are doing:
Cauldron of Souls
Inspiring Call
From there it becomes about finding what fits, what ramp and the like serve you well, what needs to be trimmed, what good stuff staples you want to play, and a lot of personal taste. Do you go with a lot of tutoring to make sure you can pull whatever you need out of your swiss army knife, or do you forego tutoring for a more unpredictable experience where you may have to 'Macgyver' together an answer?? You can add some more combos, like
Melira, Sylvok Outcast and things that work well with her, or game ending smash effects like
Tooth and Nail for
Craterhoof Behemoth (although that appeals less to me).
That's my thought process on the core of what I'd want to do with the deck. He feels like a big dude who wants to smash, with the ability to do interesting tricks to disrupt, survive, or just hit harder. Straightforward enough to have a clear game plan, but adaptable and unique to find fun new tricks everytime.