Muktol

Copying a spell doesn't count as casting a spell tough. What about phyrexian mana spells like [[Gut Shot]] or something with flashback like [[Lava Dart]]?

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First thing that came to my mind was "But I did use [[Lightning Phoenix]] in a deck that I stated as modern legal". So I raced of to check the deck....and had to replace [[Lightning Phoenix]] with something else, because I was to tired/ dumb/ whatever to read when building the deck. I did replace it with [[Chandra's Phoenix]] in my deck.
But as this wouldn't work out too good here I did a quick search and found [[Arclight Phoenix]]. Casting 3 spells should be no problem, especially when you don't have to pay for [[Lightning Phoenix]] any more.
Personally I would reduce [[Volt Charge]] to 2 cards, because you will only need them when you start "combo" with [[First Day of Class]] and bringing back your phoenix. With all the learn spells you can discard any unwanted cards and draw another card for it, so changes of finding [[Volt Charge]] even with a lower number in the deck are .

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With all the sacrificing that will be going on, you could use [[Bloodbriar]] instead of [[Blood Researcher]] (or even in addition?)

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What about [[Fireshrieker]] or [[Grappling Hook]] to provide [[Storrev, Devkarin Lich]] with double strike and thus double the number of creatures you can get back?

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[[Market Festival]] could be replaced with [[Utopia Sprawl]], which is a lot faster, but you only get 1 additional mana, and the colour has to be chosen when you cast the spell.
I'm not really convinced of [[Garruk's Packleader]] here.
Personally I would remove [[Freyalise, Llanowar's Fury]] and [[Savannah]] for something different, to make the deck modern legal. From what I've heard legacy is way to fast for such decks.

Deck and how to play decsirption is missing.
[[Deftblade Elite]] normally is a "standard" card in pauper heroic, because it is simply so good.
[[Utopia Sprawl]] doesn't give your any real benefit here.
I would use less lands and less creatures and more pump spells/ enchantments.

No [[Krark's Thumb]]?

Personally I would try to get down to 60 cards.
-7 lands
-3 [[Scute Swarm]]
-3 [[Farewell]]
-3 [[Tamiyo's Safekeeping]] +2 [[Snakeskin Veil]]
-2 [[Rune of Sustenance]]

If you find some other cards, you would be willing to remove, you could take a look at [[Hallowed Priest]], [[Ajani's Pridemate]] or [[Righteous Valkyrie]].

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Are you playing this deck in historic or standard? The problem is that arena may have some release of cards, that are not available on MTGVault (For example [[Charmed Stray]] would looooong be out of standard)

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Deck and how to play description could be a little bit more detailed ;)

Personally I would remove [[Dark Ritual]] for soem removal ([[Cast Down]], [[Doom Blade]], [[Tragic Slip]], [[Bone Splinters]]) or for some additional sacrifice outlet ([[Viscera Seer]], [[Vermin Gorger]])

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Control is always tricky as opponent, but [[Dungrove Elder]] can be a real pain to get rid of for them. It also works very well with ramp.

Wouldn't something like [[Forfend]] or [[Repel the Abominable]] also be worth a look? Advantage is that you also can prevent removal in the form of direct damage spells ([[Shock]], [[Lightning Bolt]]) with those, drawback is that they costs 2 mana

Question is, why do you want to use Tron lands, and not simple [[Wastes]] or even some artifact lands like [[Ancient Den]], [[Darksteel Citadel]] or [[Darkmoss Bridge]], which could also be used by [[Myr Incubator]]?
One option to generate infinite mana would be the use of [[Myr Galvanizer]]

There's a ton of carddraw out there, and its hard to judge what you might need. There is some carddraw related to artifacts, thyt might come in handy ([[One with the Machine]], [[Tezzeret, Artifice Master]], [[The Antiquities War]], [[Thoughtcast]]), there is cheap additional carddraw ([[Ancestral Recall]], [[Ancestral Vision]]), there is sacrifice carddraw ([[Bankrupt in Blood]]), and so on.

Personally I would rather use some tutors to get what I need on the battlefield:
[[Arcum Dagsson]], [[Fabricate]], [[Goblin Engineer]], [[Inventors' Fair]], [[Kuldotha Forgemaster]], [[Reshape]], [[Tinker]], [[Treasure Mage]], [[Urza's Saga]],

General suggestions:
[[Myr Battlesphere]]

I've made some changes after testing the dekc a little bit. One was adding [[Guul Draz Specter]] instead of [[Eternal Scourge]], and [[Vampire Nighthawk]] instead of [[Vampire Outcasts]]. The deck now runs smoother, tough I'm still not totally convinced by [[Underworld Dreams]], which has to little effect for it's price.

[[Gurmag Angler]] could be used to replace [[Catacomb Crocodile]] and [[Defile]] would also fit the swamp theme, perhaps instead of [[Mire's Grasp]]?

I think you're confusing +1/+1 counters with the +1/+1 until end of turn ability.

[[Jungle Basin]] is not modern legal.

[[Nylea's Disciple]] might be better here than [[Essence Warden]].

[[Khalni Hydra]], [[Nacatl War-Pride]]

I hate to disappoint you but haste is a static ability.

From the official gatherer oracle on [[Conspicuous Snoop]] (https://gatherer.wizards.com/pages/Card/Details.aspx?multiverseid=485462)
23.06.2020: Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keyword abilities are activated abilities and will have colons in their reminder text.

From the comprehensive rules:
702.10. Haste
702.10a Haste is a static ability.

Depending what you want to achieve, you could swap your [[Mana Leak]] for a [[Rune Snag]] (more effective in longer games), or for a simple [[Dispel]]/ [[Disrupt]] protection against removal.

You will still need something like [[Goblin Chieftain]] to pull of the [[Kiki-Jiki, Mirror Breaker]]+[[Conspicuous Snoop]] combo, as the Snoop only copies activated abilities, so Kiki's haste isn't copied.
602.1. Activated abilities have a cost and an effect. They are written as [Cost]: [Effect.]

Also you set the legality for the deck to Modern, but use [[Goblin Tutor]] and [[Goblin Recruiter]]