Muktol

[[Cubwarden]] or [[Leonin Warleader]] could be worth considering, tough it will be hard to remove something for it, as both are cmc4 cards and you wan to be this deck to be rather fast.

Works like a charm with ETB creatures like [[Kruin Striker]]

I wouldn't use [[Lochmere Serpent]] as finisher because you will need 6 mana every turn to re-cast [[Thopter Assembly]] to lock your opponent. I would rather rely on something cheap, with evasion of one sort (flying, unblockable, menace, intimidate), that brings you additional benefits: [[Nighthawk Scavenger]], [[Vampire Nighthawk]], [[Vault Skirge]] and so on.
You could use artifacts like [[Armillary Sphere]], [[Mycosynth Wellspring]], [[Renegade Map]] or Traveler's Amulet to speed up your game. Those can be fed into [[Time Sieve]] afterwards if you don't have the 5 thopters you need.

I normally would have though that this would drift more into an izzet colour combination, but [[Seeker of the Way]] is simply too good not to be taken and red had a lack of good, cheap, common prowess-creatures. Personally I also try to avoid 3-coloured pauper decks, because the mana-base seems rather unstable and difficult to built.

A short description would be a good idea in such cases, even if it's just "I'm aware that this commander is illegal, we're using house rules in our playgroup" or something like that ;-)

The problem with external prices is that you have to check each card separately, and honestly I don't want to do this when I have a comparison price here...even if this may be a bit higher than on another site. Call it laziness ;)

Didn't see that you already where using the capsule in the deck, sorry. Yes Easy Prey has the advantage of cycling, question is: How often do you want to use it, how often does it happen that you want to discard a removal for another card?

As for the changes: I would probably remove [[Flayer Husk]] and Cogworker's Puzzleknot in favour of [[Servo Schematic]] and another (cheap) card that fits into this deck, [[Traveler's Amulet]] for example. The amulet would allow you to ramp a little bit, enabling you to activate e.g. a [[Springjaw Trap]] and still cast something.
Another idea would be the usage of artifact tokens: Treasures ([[Contract Killing]]/ [[Prying Blade]] tough probably epensive), Food ([[Bake into a Pie]]/ [[Foreboding Fruit]]/ [[Giant's Skewer]]) or Clues ([[Press for Answers]])

[[Stuffy Doll]] isn't a legendary creature, so it can't be used as commander. Even if it would be, it also is a a colourless creature so you can't use cards with coloured mana-symbol of any kind in your deck.
You could tag your deck as "Highlander"-deck, as those use other building rules.

What about using [[Fastbond]] with [[Ramunap Excavator]]? When combining those with [[Retreat to Kazandu]], a simple [[Evolving Wilds]] could lead to nice combo. [[Retreat to Hagra]] could also be an option tough that is out of your colour combination at the moment.

As for the manlands/ artifacts, you could use [[Darksteel Brute]] as he's indestructible and [[Creeping Tar Pit]] would also fit into your colour-scheme and it's unblockable.
Another idea could be the use of vehicles...man your lands and let those crew the vehicles.

[[Executioner's Capsule]] instead of [[Easy Prey]]? Can serve as fodder for your [[Salvage Titan]] to help him come back into play.
[[Servo Schematic]] could also be an idea instead of [[Cogworker's Puzzleknot]]

Personally I would reduce the number of different cards you're using in favour of a more stable game-plan. Additional carddraw is a good thing, but relying on (in a deck that doesn't have carddraw as main strategy) can backfire very easily in my opinion.
Cards like [[Demystify]], that you don't use every game, should be replaced with more versatile (or potent) versions ([[Disenchant]], [[Echoing Calm]], [[Heliod's Intervention]], [[Leave No Trace]], [[Light of Hope]]) or moved into the sideboard.

Here are some additional suggestions if you want to replace cards in your deck:
[[Empyrean Eagle]], [[Jubilant Skybonder]], [[Sephara, Sky's Blade]], [[Thunderclap Wyver]],
[[Favorable Winds]], [[Rally of Wings]], [[Battle Screech]]

Just be aware that the 2 tokens spawned by [[Hero of Bladehold]] will not activate [[Hellrider]]'s ability.

With all the spells that also force you to discard, you could add some of the madness-cards that came with Eldritch Moon:
https://www.mtgvault.com/cards/search/?q=madness&searchtype=text&ps=20

There are so many ramp-options out there, that it's hard to keep track of. My favourite would be defender-ramp, using [[Axebane Guardian]], [[Overgrown Battlement]] and a bunch of cheap defenders like [[Order of the Stars]] or the classic ramp in the form of [[Harrow]] or [[Arbor Elf]] + [[Utopia Sprawl]]

A short deck- and how to play description wouldn't hurt anyway ;)
Personally I would use other ways to get [[Progenitus]] into play than [[Garruk, Caller of Beasts]] (Which is currently the only way you can get him into play, unless I've overlooked something). [[Elvish Piper]] would be the most prominent, but there are alternatives to it: [[Iwamori of the Open Fist]], and [[Dramatic Entrance]]. [[Fierce Empath]] can be used to get Progenitus into your hands

[[Kaya's Wrath]] could be an option (at least sideboard) against aggro/ swarming decks.

I've recently spoken to my friend about this deck, especially when I mentioned [[Conclave Mentor]] to him. He seemed very interested in that creature, and said that he wanted to add it to his deck. I'm really interested with what he will come up our the next gaming-night (which will unfortunately take some time).
Personally I would go for [[Conclave Mentor]] or [[Barkhide Troll]] as replacement for [[Enduring Scalelord]] and [[Seal Away]] as removal. I will sent him your suggestions, let's see what he does with them ;)

Don't know if your friend is still playing but: Ikoria brough [[Bastion of Remembrance]] (basically [[Blood Artist]] 4-8, but harder to remove) and [[Serrated Scorpion]], which might fit into here.
Personally I would also add something that lets you sacrifice your creatures and benefit from this. There are numerous options for this, but [[Bloodflow Connoisseur]] or [[Bloodthrone Vampire]] would be some of the cheaper ones. Some carddraw in the form of [[Village Rites]] might also be an idea.

War of the Sparks brought some good landfall/ proliferate cards that you could add here:
[[Evolution Sage]] (Works like a charm with [[Nissa, Who Shakes the World]]'s ultimate), [[Pollenbright Druid]], [[Contentious Plan]] and [[Courage in Crisis]] could be worth a look.

A short deck- and how-to-play description would be a good addition. If you don't know what to write, you might take a look at
https://www.mtgvault.com/muktol/decks/why-you-should-add-description/
[[Ball Lightning]]/ [[Groundbreaker]] come to my mind when talking about fling. [[Brion Stoutarm]] could also be an idea, tough he's out of your choice of colours. [[Elvish Mystic]] could be replaced with [[Utopia Sprawl]]. could also help you with mana-fixing.