Muktol

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/

Thank you for bringing Ruin Crab to my attention. Some time ago I was playing around with Hedron Crab, some low cmc creatures and [[Mirrorweave]] to build a U/G mill deck. I have replaced some of the creatures there with Ruin Crab, which will further increase the chances of the deck.

I would replace [[Benalish Marshal]] with [[Knight Exemplar]].
[[Valiant Knight]] could be used instead of [[Embercleave]], if you prefer mass-doublestrike instead of a single creature. Downside is that you lose a historic spell that activates [[The Circle of Loyalty]]

What about [[History of Benalia]], [[Valiant Knight]] and especially [[Knight Exemplar]]?

What about [[Untethered Express]]?

What about [[Narnam Renegade]] and [[Wasteland Viper]]. The first is no snake but a possible 2/3 for {G} isn't to shabby.

Personally I would try to reduce the 1-offs you have and go for a more constant approach: Cards that you want to draw as often as possible 4 times, cards that you want to draw once in the game 3 times, and cards you are able to search for 1-2 times.
As for the ETB triggers, and to protect your creatures, I can recommend [[Ephemerate]]/ [[Teferi's Time Twist]] and [[Ghostly Flicker]]. Maybe also use [[Saving Grasp]] instead of [[Dramatic Rescue]] as it allows you to re-cast the spell, a big bonus in longer (multiplayer) games.

Thank you for the suggestion. I removed 2 [[Doom Blade]] for 2 [[Final Payment]], lets see what the beginners prefer ;)

My knowledge of the commander rules is that planeswalkers, like [[Teferi, Master of Time]], aren't allowed as commanders. Only PW's like [[Aminatou, the Fateshifter]] where it says "XYZ can be your commander" can be used as such.

Personally I would remove [[Heir of Falkenrath]] and [[Vampire Envoy]] in favour of [[Vampire Nighthawk]] and [[Bloodthirsty Aerialist]]. Also perhaps [[Essence Extraction]] for some hard removal like [[Doom Blade]].

I was thinking to take either Gods Willing for protection or Bankrupt in Blood for carddraw, but without some tests it's hard for me to judge which one would be needed more. [[Thraben Inspector]] is a good idea as it adds another creature, but less carddraw. Will have to see to that.

[[Leyline of Sanctity]] is at least sideboard material, if I don't put it into mainboard. [[Leyline of the Void]] shouldn't keep my creatures from triggering as it says "opponents graveard" and all my cards interact with my own graveyard.

No, this is purely meant for kitchen table play, I added the proper tag.

Maybe [[Dust of Moments]] (or [[Timebender]] if you prefer a creature, tough [[Dust of Moments]] will work better with Narset's Reversal) to increase the counters on [[As Foretold]].
Personally I would also add something like Apostle's Blessing to protect your [[Isochron Scepter]] or your [[Aetherling]]

I would either go for vehicles or servos here, but not both. You need a [[Metallic Mimic]] for [[Animation Module]] to work and have to pay mana every time you want an additional token. Also the servos are, in my opinion, not really helpful when activating your vehicles, the only thing they can help you with is to serve as chump-blockers.

Personally I would rather do an aggressive vehicle deck:
Remove 4 [[Metallic Mimic]] 3 [[Master Trinketeer]] and 3 [[Animation Module]] to add 1-2 [[Chief of the Foundry]], 1 [[Depala, Pilot Exemplar]], 1 [[Inventor's Apprentice]], 3 [[Veteran Motorist]] and 3-4 additional vehicles like [[Mobile Garrison]], [[Renegade Freighter]], [[Smuggler's Copter]] or [[Untethered Express]]

[[Lightning Strike]] could be replaced with [[Dispatch]] or [[Galvanic Blast]] as you should have enough artifacts to make the metalcraft work.

+1
Personally I would remove/ sideboard [[Spark Trooper]] and [[Tajic, Blade of the Legion]] and add something of the following:
[[Captain of the Watch]] or [[Preeminent Captain]] if you want a strong soldier theme/ synergy;
[[Signal Pest]] if you want a little bit more speed;
[[Skyknight Vanguard]] if you want constant creature-production;
[[Hellrider]] or [[Odric, Master Tactician]] when you feel that your opponent has a defence that is difficult o penetrate (Always a good sideboard option)
I would also replace [[Sure Strike]] with e.g. [[Pride of Conquerors]]/ [[Charge]] (more aggro), [[Apostle's Blessing]]/ [[Brave the Elements]]/ [[Center Soul]] (protection) or by [[Brute Force]]/ [[Infuriate]]/ [[Titan's Strength]]

What about a creature and [[Ethereal Armor]] for a little bit more offensive play? [[Brine Giant]] for example.