Muktol

A deck- and how to play description would be a nice addition ;)
You have a lot of creatures that let you sacrifice other creatures, but few ways to gain something that you can sacrifice into these, without loosing something valuable. [[Geralf's Messenger]], [[Nether Traitor]], [[Reassembling Skeleton]] or [[Bloodghast]] could help you here.

I had [[Snakeskin Veil]] in the mainboard, but went for [[Emerge Unscathed]] to get protection. Helps to protect or deal damage to your opponent. The reason was that [[Star Pupil]] and [[Servant of the Scale]] have sort of protection of their own, as their power isn't lost. But I re-added [[Snakeskin Veil]] to the sideboard, when going against removal heavy decks.

I have reworked the deck somewhat and finally had the time to test this. [[Star Pupil]] and [[Servant of the Scale]] are a real pain in the ass for an opponent because their power isn't lost (if they aren't the last creature). [[Skyhunter Skirmisher]], which loves to take their counters, can deal massive amount of damage, and often can simply bypass opponents defence.
The only thing I'm missing would be some carddraw (I threw in [[Palace Sentinels]]) and/ or some way to proliferate more often, but sadly thinks like [[Karn's Bastion]] or [[Contagion Clasp]] are not pauper legal. I was looking at [[Urban Daggertooth]], but enabling enrage in this deck is rather difficult.

Having a formula (Or a strategy, or a game plan) is never a bad thing. But I will copy a passage, I wrote in an article deck some time ago:

[quote]
Play cards 4 times
You have a strategy and you have some cards that you want to draw to win this game, those cards are key-elements to your plan. So if your deck and strategy is built around certain keycards you can question yourself “how often do I want to have those in my hand or on the battlefield?”. The answer in most of the cases will be “as often as possible” so have as many of those in your deck as possible: 4 times. If it is part of your strategy to have e.g. a counterspell on your hand in turn 2, you should not just play one type of this spells 4 times but two or even more.
Cards that you don’t want to have on your opening hand, can be reduced to 2-3 copies. This ensures that you have a chance of drawing them later on when you need them. The same goes for legendary cards because you normally don't want to have more than one on the battlefield and perhaps a second one on your hand. If you have a high number of spells that let you draw cards, or you're using cards that let you search for other cards (so called "tutors"), you can reduce those numbers to 1-3.
[/quote]

If builders normally deviate from this basic rule of deckbuilding I ask them why they did so. There may be some reasons, for example existing cardpool, unwilling/ able to buy/ trade new cards, or similar things. This would be one of the things, you could add to your deck description. Information why you added a second deck to the sideboard would also be valuable, is this pair meant to duel, is the other one a templated from the internet, and so on. :)

A deck- and how to play description would be a nice addition. :)
Perhaps you could also include an explanation why you're using nearly each card only twice?

+1
Wouldn't something like [[Clattering Augur]], [[Dread Wanderer]], [[Gutterbones]] or [[Sanitarium Skeleton]] be better than [[Jungle Creeper]]? [[Ravenous Squirrel]] and [[Bloodflow Connoisseur]] ([[Carrion Feeder]] could also be used here) will be the muscles of the deck, so you need cheap creatures to sacrifice and return.

Some other suggestions, that come to my mind:
[[Smallpox]], [[Tragic Slip]], [[Bloodbriar]], [[Mortician Beetle]], [[Undercity Informer]] (Convert the deck into a mill-deck)

A deck- and how to play description would be a nice addition. :)
[[Sarkhan's Triumph]] could be used to search for dragons you need.

[[Arcbound Bruiser]] could be replaced with [[Arcbound Mouser]] or [[Arcbound Prototype]].
[[Energy Chamber]] could be replaced with [[Contagion Clasp]] or [[Karn's Bastion]], which would enable you to proliferate instead of adding a single +1/+1 counter to a creature. I would also remove [[Titan Forge]], as it doesn't fit into the gameplan for me, and add some protection like [[Emerge Unscathed]], [[Gods Willing]] or [[Shelter]], which can be used to protect your creatures (Exile and -X/-X still work on indestructible) or enable them to bypass any defense your opponent still might have after a board-swipe.

Personally I would also either remove the thron lands or add something that lets you search for them. With the suggestions mentioned above this would leave you with only [[Darksteel Plate]] as high-mana creature, which easily could be replaced by [[Darksteel Plate]].
If you want to use high-mana cards I would take a look at [[Arcbound Overseer]] or [[Contagion Engine]].

You might need more cheap cards that let you discard when you want/ need to:
[[Lightning Axe]], [[Thought Courier]], [[Cathartic Pyre]], [[Dangerous Wager]], [[Izzet Charm]] or [[Thrill of Possibility]]

+1
What about [[Orzhov Charm]] or [[Revival // Revenge]] instead of [[Elixir of Immortality]] or [[Trading Post]]?

Thank you for the clarification. A classic case of "Read the fucking card" ;-)

I'm not a big fan of 3-coloured decks, neither in pauper nor in modern. But if I would have access to blue, I would at least give it a try instead of [[Lead the Stampede]], because I think it would draw consistently more cards.

I finally was able to do the testgames I wanted to.
[[Lead the Stampede]] draws you 2-3 creatures in average, rarely less or more.
I wasn't quite convinced by [[Virulent Sliver]], because if you have 9 poison counters on your opponent, and he manages to get rid of this sliver, you basically start at 0, until you're able to draw/ play another one. This can wreck the gameplan quite a bit.
[[Sidewinder Sliver]]'s flanking ability is very potent and can really turn the tides or even prevent your opponent from blocking.

What about [[Zombie Infestation]] and [[Bloodbond March]]?
I was playing around with a similar idea, as I was looking for something like [[Extirpate]] or [[Surgical Extraction]], that lets you remove all cards of a given name, but not into exile, but rather into the graveyard.

Not really belonging to this deck but I didn't know how to reach you otherwise.
Do you know if there is a card like [[Extirpate]]/ [[Surgical Extraction]] that lets you name, search and discard all cards with this name into your graveyard (Rather then exile them)

Always a pleasure to get feedback and learn the thoughts of other players and builders :)

I know that I'm underestimating many new players, but I've had some situations with them that made me overcautious in the end. So here are my own concerns when it comes to burn (or infect or RDW)

You have to accept that your lifepoints are nothing but another resource... something that is difficult for many layers, not to speka of beginners.
Like control, you have to know (or quickly learn) which creature to remove, which you can let on the battlefield and when it's time to simply try and burn your opponent to cinders.
Also this budget burn deck features very few 1mana/ 3 damage spells, for the obvious reason: They are expensive ($). So it might be harder to defeat your opponent with this one.
Last thing I want to throw in is that it's normally no fun to play against burn.

No problem. Two rectangular brackets before and after the card name. Tough misspelled names or such with apostrophes won't work
[[CARDNAME]]
[[Faith's Shield]]

The very first deck I played at a game store was mono white humans, followed by black/ red vampires. But I started to note down prices of decks, before adding special lands. This showed that most mana bases for two modern legal coloured decks I built made about 50% of the decks total value. The first thing, that came to my mind when reading your question, was rarity, and the quick evaluation from some of my old decks and the 2 linked sites seemed to fortify my assumption. Even many mono coloured decks today will want to play some special lands, like fetchlands or something that boosts you mana, manlands, and so on.

I would have placed this question in the "MTG General Discussion" forum.
Pretty normal for modern legal decks, which use 2 or more, colours that the mana base makes up 50% and more of the decks value, if you use competitive lands.
The problem is that everybody needs lands.
When you look at the metagame (e.g. https://mtgdecks.net/Modern) and analyse the decks, you will quickly find that mono-coloured decks are a minority. 3 out of 26 decks (I only counted for a meta of 1% or higher, below it might be a little different but not much) and 14 out of 26 decks are 3-coloured of higher. Why is that so? Mono coloured decks play very fluid, but have the problem that they are limited to one colour. You can't play every strategy you like or be prepared for everything with one colour, and if you could, the spells would be incredible expensive to cast or have other major drawbacks. 3 colours allows for even a wider approach in strategy, but in my opinion, here it starts to get tricky with the mana base, tough it's doable.
A mono coloured deck uses basic lands, no problem. A 2 coloured decks normally doesn't use more than 2-4 basic lands, the rest is dual-, fetch-, or support-lands. 3 coloured decks often use both sets of dual-lands to get a stable mana-base, because there are no competitive 3-coloured lands!, so the demand for those lands is even higher. If you look at (https://www.mtgtop8.com/format?f=MO&meta=220&a=) 8 out of 10 of the most played cards are lands.
Last problem is the rarity and availability. Nearly all of the competitive lands used for mana fixing are of rare or mythic rarity. So you have 1 chance per booster to get this card, not including alternative arts or foils. I would have to look at the data of my collection at home, but I'm pretty sure that you don't get much more than 5 of those lands out of a 36 booster brick.
So we have a huge demand, and a low availability.

Forgot about [[Thermo-Alchemist]] (and attacking), so it's 0-2 mana to activate Spectacle and 1-4 mana to play both cards.