Muktol

I'm a little confused because in my understanding [[Leyline of Sanctity]] helps against most burn, discard, mill and so on spells, but not against infect, nor does it help you with combat damage (something I'm relating to the term "combat based decks"). It "only" prevents your opponent from using any spells where he needs to target a player (e.g. [[Lava Spike]] but not [[Thermo-Alchemist]]'s ability). It doesn't help against proliferate (e.g. [[Courage in Crisis]]) as there is nor "target" in the proliferate text.

You would need a way to interact with the threats your opponent puts on the board, or that help you to protect you from such things.
Autumn's Veil, [[Dawn Charm]], [[Mana Tithe]], [[Rebuff the Wicked]], [[Aegis of the Gods]], [[Leyline of Sanctity]], [[Teyo, the Shieldmage]]. Those are all rather defensively played cards.

[[Expedition Map]] and/ or [[Circuitous Route]] to quickly search for missing lands?
[[Hangarback Walker]] could be used to sink the excess mana into, to keep you alive, when you run out of [[Fog]] cards.

+1
[[Thalia's Lieutenant]] could be an idea, the only creature that it doesn't interact with would be [[Preeminent Captain]].
[[Brave the Elements]] is another card I can only recommend.

[[Everflowing Chalice]] and [[Astral Cornucopia]] are relicts from the time the deck contained [[Power Conduit]] and [[Chronozoa]] as counter-storage. The problem with [[Everflowing Chalice]] and [[Astral Cornucopia]] is that I don't have anything to use massive amounts of mana generated by those artifacts, be it colourless ([[Everflowing Chalice]]) or coloured ([[Astral Cornucopia]]), so this is propably a card I will remove at all.
I took a look at your deck and added [[Trophy Mage]] to my side/ maybeboard and 1 [[Cyclonic Rift]] instead of [[Negate]]. Thank you for this suggestion.

I finally decided to throw the "modern pauper" legality away and focus on real pauper.
I rebuilt the deck, and now I'm also using [[Rancor]], which can be a tough one to crack for your opponet when used with [[Skarrgan Pit-Skulk]]. It also makes the combination of [[Timbermaw Larva]] (one of the few surviving cards from the old version) and [[Ram Through]] rather dangerous. Attack with the trampling larva, target a 1/1 with [[Ram Through]] and deal massive damage, before your creatures even start do deal damage themselves.
I also was able to finally test the deck against my other pauper brews, using Coakatrice, and it works very well. The only things so far (I'm not completely through with my test-list) that gave me some trouble where Golgari Madness/ Hellbent (40% Winrate), Izzet Prowess (30%), monoW Equipments (30%), Orzhov Enchantments (20%) and Selesnya Enchantments (15%).

Deck- and how to play description are missing.
Healer's Hawk, [[Kor Duelist]], [[Stone Haven Outfitter]], [[Bone Saw]], [[Shuko]], [[Ancient Den]]

@ Puschkin:
I'm equally happy to see a familiar name that is still working on this site ;)

Not essentially quicker, but normally cheaper ($) and less frail to disturbances of the mana-base. The downside is that no colour has access to all spells and ability's. For example artifact and enchantment-removal (Always the first thing that comes to my mind when talking about this): Green and white is really good at knocking out artifacts and enchantments, red can do it with artifacts, but black and blue lack the ability to remove such things, but they have other strengths.
If you play magic the knowledge of cards and colours will come quickly, and this will also help you to get a feeling for what colour-combination is possible and makes sense. And if you struggle, simply ask for help. A "Help" tag on a deck shows the shows the users here that you have some questions....which are best written down in a deck-description ;)

+1
If you need to get key-cards in your hand then [[Read the Bones]] could be of interest here. It costs 1 more mana than [[Sign in Blood]] but allows you to scry 2 before you draw 2 cards.
[[Smallpox]] could also be an option as removal as it attacks all resources available to players. You have a way of playing around the sacrifice part, but not the rest, but you can decide when to play it and thus are better prepared for it's effect.

The deck-description could be a little bit more detailed.
Personally I'm no big fan of single cards that ruin a decks higher legality, like [[Innocent Blood]] in this case. You one day might want to take this to a local tournament and can't, because of this one card.
My own life gain/ drain decks use white as second dolour for a very simple reason: It gives you access to many interesting cards like [[Cruel Celebrant]], Ajani's Pridemate, [[Sorin, Vengeful Bloodlord]], [[Drana's Emissary]], [[Final Payment]], [[Oblivion Ring]], artifact/ enchantment removal, only to name a few things.
Another approach could be the sole use of zombies with [[Undead Augur]] and [[Diregraf Captain]]
If you want to stay mono black then there are still some interesting cards: [[Orzhov Enforcer]], [[Supernatural Stamina]], Bastion of Remembrance, [[Bloodthirsty Aerialist]], [[Sign in Blood]], [[Driver of the Dead]].
If you manage to narrow down the tribals you're using than the new card [[Raise the Draugr]] could be of interest here.

+1
Since when is [[Mutavault]] pioneer-legal?
To effectively use Ajani's Pridemate ability you need [[Regal Caracal]] on the board, otherwise it will be just a 2/2 cat for 2 mana. I would either include some other cats that have lifelink or remove him at all. Personally I love [[Leonin Warleader]] in combination with the Pridemate, especially if you have some ETB triggers.
I would perhaps try to reduce the number of creatures you're playing to add 2 kind of spells: Card-draw and removal. Regal Caracal command is a versatile card, but alone it won't be enough. Cards like [[Oblivion Ring]], [[Prison Realm]], [[Seal Away]] or [[Pacifism]] could be an idea. As for the carddraw [[Adventure Awaits]], [[Camaraderie]] or [[Rogue's Gloves]] could be an idea.

We've used Wanderer's Strike in the original version and, as far as I remember, it proved to be to slow and to expensive. But let's throw it into the sideboard, and see what the player will say himself :)

I was lucky enough to get Urza Gatherer installed on my PC some time ago, as nowadays you can only use it as browser/ mobile ap. Nevertheless, it works really well when managing a collection.

+1
[[Wee Dragonauts]] isn't a dragon, but it would fit into the deck for it's mechanic.
Another card that comes to my mind would be [[Temur Battle Rage]], because instant double strike is always a devastating option.

Personally I prefer Urza Gatherer (https://www.urzagatherer.app/) to keep track of my collections

Personally I would add more possibilities to protect you commander: Champion's Helm, [[Mask of Avacyn]], [[Darksteel Plate]], [[Hammer of Nazahn]] or [[Shield of Kaldra]] as removal, and especially mass-removal is quit ecommon in commander.
To increase the number of counters you put on your commander every turn cars like [[Doubling Season]] (and it's variants), [[Contagion Clasp]], [[Forced Adaptation]] or Karn's Bastion

A deck-and how to play description would be a good addition.
[Imaginary Pet]], [[Greenbelt Rampager]], [[Thrummingbird]], [[Bred for the Hunt]], [[Colossal Majesty]], [[Renegade Krasis]]

Personally I would reduce the number of [[Pelakka Wurm]] and [[Penumbra Wurm]] by 1, to add some more ramp. [[Yavimaya Elder]] or [[Viridian Emissary]] would fit the theme and would be budget. [[Solemn Simulacrum]] would also be an option, but I think this will be out of the deck's budget.

+1
[[Manifold Key]], [[Voltaic Construct]], [[Voltaic Key]] or [[Voltaic Servant]] could be used to untap your Witch's Oven an re-use it.
Another interesting card could be [[Marauding Blight-Priest]] (or [[Cliffhaven Vampire]] or similar lifeleech cards)

How do you plan do deal with decks that don't attack you (mill) or force you to lose life (which doesn't count as damage) or have artifact/ enchantment/ creature removal?