Muktol

If you want to play a little more aggressive [[Rat Colony]] and [[Swarm of Rats]] could be useful.
[[Typhoid Rats]] can serve as indirect removal, while [[Doom Blade]] can take the direct treats your opponent puts on the field.
Last [[Bad Moon]] could be used to strengthen all your rats a little more.

Am I this predictable?

[[Thraben Doomsayer]] could be used instead of [[Gather the Townsfolk]] if you want a more constant token production.
Another card I can recommend would be [[Student of Warfare]], tough he's expensive to level up.

A short deck- and how to play description would be fine, even if there is a youtube link. Some of us still prefer to read, instead of watching a video ;)
Drawback on [[Indomitable Ancient]] is that it's not standard-legal.

Personally I would trade [[Metallic Mimic]] for [[Corsair Captain]]. The captain has the advantage of strengthening all creatures, not only the ones who enter after him.

I would rather try to find mechanics (Fear, Intimidate and so on.) that are underrated, but even this will be hard.

Yes, but that should only be relevant if your opponent has more creatures than you (e.g. Elves or Goblins)

In my opinion it's hard to rate a card in general as many cards only show their full potential in combination with others, but do very few on their own. So to me, except for [[Ashiok, Dream Render]] (which I've seen in some MTGA sideboards while I was active there), the cards you've listed until are underrated/ overpowered only for 1-2 decks, but others would never even think of adding them.
For example [[Ancient Greenwarden]] works very well in a standard landfall deck, but would ultimately loose in modern to [[Crucible of Worlds]] because it's faster to play and can be used by more decks. Another example would be [[Midnight Guard]] which is a creature with pseudo vigilance, but in combination with [[Presence of Gond]] he reaches a whole new level.

I know it doesn't fit the colour scheme perfectly, and it's ability is rather expensive in comparison to [[Steel Overseer]], but what about [[Gavony Township]]?

Sadly [[Artful Dodge]] is blue, because it would fit in here perfectly. [[Nightbird's Clutches]] would be a red alternative, tough it only affects 2 creatures and the flashback is rather expensive.

What about [[Mirrorweave]] to turn all those tokens you create into [[Seven Dwarves]] before you attack? Would be kind of an overkill, but it would fit the "Mirror" theme of the deck.

A short deck and how-to-play description would be a nice addition.
Personally I think 8 changelings should be enough to activate the abilitys of your party people and thus would remove [[Stonework Packbeast]] to add some equipment to give your creatures either evasion or some additional punch: [[Cobbled Wings]], [[Horned Helm]] or [[Bonesplitter]] would be my "standard" choices in pauper.

Why not use the confusion part to your advantage? Personally I would build (/play) this as a blue artifact deck, which has [[Arcane Adaptation]] + [[Liliana's Contract]] as surprise win-con. Use your creatures to ramp, draw and search for your key-components, or have them as protective barrier around you that replace themself with tokens.

Against boardswipers you could use [[Hissing Iguanar]], at least in the sideboard.
To get rid of your colour problem 2 basic forests and plains, and some searchlands like [[Evolving Wilds]] might be an idea.
Personally I would favour [[Goblin Gathering]] over [[Dragon Fodder]] or [[Krenko's Command]], because it gets stronger the more you play it. I would also include some carddraw, e.g. [Tormenting Voice]], to make sure you draw enough cards, as low CMC decks tend to run out of handcards (and thus options) rather fast. Last, [[Goblin Grenade]] is pauper legal, so if you're looking for a cheap, strong, additional, finisher, this might be an idea.

I would rather concentrate on producing my own treasure tokens than relying on my opponent to play along, because that normally backfires. And no matter what, I would use a fourth copy of [[Revel in Riches]] because it's not legendary, your opponent will try to get rid of it once he see's your plan and, if he can't, you can use it multiple times on the board.
What about [[Pitiless Plunderer]] in combination with your sacrifice-creatures and [[Ruthless Knave]]? [[Deadeye Plunderers]], [[Prying Blade]]?

A short deck and how to play description would be a good thing.
Personally I would cut [[Demonic Tutor]] and [[Sol Ring]] to get this to modern legality. You're running no removal, beside [[Butcher of Malakir]] and [[Dictate of Erebos]], so I would first invest in some of those, to make sure your vampires come to your opponents throat.

What about [[Rogue's Passage]] to make your finisher unblockable?

When you need help a short description on WHAT you need help with would be useful.

I was toying around with the idea of 3-4 [[Undergrowth Champion]] instead of [[Augur of Bolas]].

I'm not really convinced from [[Sakura-Tribe Elder]]. When you Mirrorweave all creatures into Elders and sac some of them you have enough lands, but nothing that benefits from the land-drops.

I had [[Scapeshift]] in the deck before I started fiddling around with it a little bit, but 8 spare mana are hard to achieve if you want to keep your ramp to activate the crabs.

As for the chance of a backfire, this might happen in the second game, normally you play and fetch in an instant, because you need colour-fixing or want to thin out your lands. But even if he spares 1-2 fetchlands [[Khalni Heart Expedition]] and/ or [[Ghostly Flicker]] still should bring more landdrops than he might be able to produce.

For now I will do the following:
-2 Crabs
-1 [[Hornet Nest]]
-3 [[Saproling Migration]]
+3 [[Undergrowth Champion]]
+3 [[Cobra Trap]]

I normally don't ask for help, especially on a discussion where the deck doesn't belong to me, but...if you got the time, would you take a look at :
https://www.mtgvault.com/muktol/decks/ug-mill/