Muktol

Another option would be [[Zada, Hedron Grinder]] + [[Venerated Rotpriest]] = Instant death. Tough this would need a red splash.

[[Venerated Rotpriest]] + [[Wild Defiance]] = pain

[[Skyhunter Skirmisher]] instead of [[Leonin Skyhunter]?

What about [[Colossus Hammer]]? I would also include something to protect against removal, like [[Darksteel Plate]] for example.

[[Etched Champion]]

Personally I would remove [[Atog]] and [[Paradise Mantle]] and focus more on enchantments. I see some other issues with cards in the deck, but this would be my first step.

As for [[Paradise Mantle]]: A creature equipped with the Mantle works just like a land then, with one bid difference: A creature has summoning sickness, while a land can be tapped the turn you play it.

Graveyard hate is a part of almost any sideboards, some decks even play it mainboard, so yeah, a replacement for [[Myr Servitor]] would be an idea. What about some affinity creatures? [[Frogmite]], [[Myr Enforcer]], [[Steelfin Whale]] (or [[Gearseeker Serpent]] which you already mentioned)?

Personally I would rather try to target a bridge-land with [[Kenku Artificer]]. Anyone in need of an Indestructible 3/3 flyer? Yes please!

[[Sylvok Lifestaff]] vs. [[Bonesplitter]] is a question of aggro vs. midrange, and as this decks looks more like a midrange deck, [[Sylvok Lifestaff]] would fit better here.

The only real thing in terms of mass removal in pauper (in this colour-combination) would be [[Fiery Cannonade]], question is if 2 damage will be enough... which I doubt. If you want to have something to deal singe target damage then [[Orcish Vandal]] or [[Makeshift Munitions]] could be worth a look.

[[Ponder]] could be replaced with [[Thoughtcast]].

Wha about adding a 3rd colour? I'm not really a fan of 3- coloured decks, but I saw what pressure my Naya Metalcraft deck could build up, and it was really fun to play. Any of the remaining colours could add to the decks strategy:
Black [[Glaze Fiend]], [[Vampire's Kiss]], [[Deadly Dispute]], [[Vault Skirge]] (Phyrexian mana!)
White [[Ardent Recruit]], [[Auriok Sunchaser]], [[Court Homunculus]], [[Glint Hawk]], [[Greatsword of Tyr]]
Green [[Carapace Forger]], [[Mirran Mettle]]

[[Experimental Synthesizer]] could be something for the deck as it gives you additional draw, can be searched with [[Trinket Mage]] and can generate you a 2/2 token if you desperately need one.

It would be interesting to get a short summary or hear which cards performed well in those 3 matches and which didn't.

[[Order of the Stars]] is one of my favourite defenders for such decks as it can stall anything that doesn't have trample or is an artifact.
[[Perimeter Captain]] or [[Stalwart Shield-Bearers]] could be an option instead of [[Fortified Rampart]], tough the Captain might be a budget problem.

Yes, I've misread, you're absolutely right. At the moment I'm at home for some days and obviously my brain is going numb. ;-)

[[Skullcage]] doesn't seem to fit the deck for me, with all that discard you will want to keep an opponent on zero cards for most of the game. [[Megrim]] or [[Shrieking Affliction]] could be a replacement for this.
[[Scepter of Fugue]] and [[Nihil Spellbomb]] are just some general suggestions.

Duel Commander seems to use the "normal" commander rules for deck-building, like colour identity... or singleton use:
With the exception of basic lands, no two cards in the deck may have the same English name.

There should be enough wolves/ werewolves to fill up the ranks of the deck. For the support side of your deck keep in mind that you will bee playing against a single opponent, so cards normally effective in commander, like [[Blade of Selves]], won't be as strong in duel commander.

Care to explain what DUAL Commander is? The only thing I could find was something about DUELL Commander, which is basically commander deck focused on 1vs1 instead of multiplayer.

The new "Toxic" keyword and the new Phryexia expansion in general could also add some interesting cards to the deck:
[[Crawling Chorus]], [[Infested Fleshcutter]], [[Jawbone Duelist]], [[Skrelv's Hive]], [[Skrelv, Defector Mite]], [[White Sun's Twilight]], [[Experimental Augury]], [[Prologue to Phyresis]], [[Basilica Skullbomb]]

Some people have a friend/ fanbase, they get more comments, others... simply need luck.
Normally I give detailed comment only when someone has a proper deck-description, decks without a description get no comments and likes at all or, if I REALLY like the concept/ idea, only some quick card suggestions, without any additional words. Guess you got lucky.

[[Remember the Fallen]], [[Emerge Unscathed]] and [[Contentious Plan]] come to my mind when seeing this deck.

[[Order of the Stars]], [[Door to Nothingness]]

[[Carrion Feeder]], [[Mortician Beetle]], [[Gixian Infiltrator]], [[Hordeling Outburst]]
A deck-description would be a nice addition to your decks :)

I have tested the original list, but not this one.

[[Talon Sliver]] came to my mind because it was mostly using the shapeshifters in defensive situations and first strike should allow them to survive a little bit better. The question was: Add a 4th [[Sinew Sliver]] or something new, and I quickly looked at my sliver-list and found this card. [[Crypt Sliver]] could also be an option in terms of survival tough it doesn't add to the decks combat abilities.

As for the lands: I rarely had the problem of being colour-screwed, and even the situations where I had problems with mana in general where very few. Also I really love the New Capena search-lands (like [[Obscura Storefront]]) and them it instead of [[Evolving Wilds]] in every multi-coloured pauper deck I have. And they are cheaper than [[Ash Barrens]].

@wickeddarkman
I took a look at [[Venomous Changeling]]. Personal feeling is that it would fit into the deck and it wouldn't fit into the deck at the same time. On one hand the deck needs at least 1 Shapeshifter on the battlefield boost [[Griffin Rider]], on the other hand it wants as many Shapeshifters on the field for [[Smitten Swordmaster // Curry Favor]].
[[Venomous Changeling]] is way better than a 1/1 any of the other shapeshifters in this deck. But Deathtouch is an advantage and drawback at the same time because it keeps opponents from attacking but it will draw and removal an opponent has. And with 3 mana its also on the upper scale of the deck.

[[Ghyrson Starn, Kelermorph]]?
A short deck-description would also be a nice addition.

Feel free to do so. I would happy, if you manage to play the deck, if you could give me some feedback on how it worked out or what you changed :)

In my tests I got the following results:
Boros land destruction 5-2
Dimir defensive mill 6-1
Mono black control 4-3
Mono green stompy 3-4
Mono red Red reck wins 3-4
Orzhov life gain/Drain 4-3
Selesnya tokens 3-4

If you want to print some proxies to give cards a try I can recommend https://www.mtg-print.com/. The got good quality images of the cards (in English) and even have some other language-version of the cards available (Although not in the same image quality). I know some people vote against proxies, but I think they're a great way of trying out different cards, before you actually buy them.