Muktol

Each decks should include a deck- and how to play description. The deck description should involve things as the basic idea why you did build this deck, if there's any story behind it, budget, certain cardchoices, especially if they deviate from common lists, legality, or any other information you can give others that will look at your deck. Best do this while you are building the deck because after some days important information's simply may not be remembered.
The how to play description is crucial for beginners. An experienced or expert builder can normally take a look at your deck and see how it should work, but there also are a lot of beginners out there that maybe want to take a look at this and compare it with their own ideas/ decks. Even for more or less standard-decks there should be a description just because of this.
By using deck-tags you can avoid to put unnecessary information into the deck name and thus making it too long. The tags also allows you to filter the decks you have made for a certain type, very useful if the number of decks you've build here steadily grows and grows.

After that we can start working on the deck if you want to.

Greetings
Muktol

With the high number of defenders I would use "Doorkeeper" as second mill-option and remove "Traumatize" instead.
The problem with "Midnight Guard" is that you need 3 (4 if you want an endless interaction with "Ornithopter") components for your plan to work. And the Guard is highly risky to play simply because you have to protect him one turn and he can (and will) be hit by any removal your opponent has left. Basically I would cut some defenders to add control and carddraw spells.
Another way would be to splash green to get access to defenders like "Axebane Guardian" or "Overgrown Battlement" and use spells like "Increasing Confusion" with 'pay {x}' effects. This would also enable you to use "Assault Formation" as backup-plan.

One of my all-time favourites as defender is "Order of the Stars". Cheap mana-costs and flexible protection makes this card a real winner. "Kaijin of the Vanishing Touch" is another good defender that makes things for your opponent a little more complicated.

Greetings
Muktol

Should the deck stay modern legal? Should it be just any legality (kitchen table)?
Basically the plan to use elves to produce mana is a good one in an elf deck. The only problem is that you need a lot of elves to produce mana and cards like "Elvish Archdruid" only work with elves and only strengthen elves. The same is true for "Krenko, Mob Boss" or "Goblin Rabblemaster". So what I would do is look at cards that provide mana based on the number of creatures you control and buffs that work for all your creatures. For example "Battle Hymn" or "Dragonrage" and "Overwhelm" (or "Obelisk of Urd"). A second way to ramp with elves would be to use those that let you search for lands.
I also would try to search for cards that work with all creatures and not only a single tripe, e.g. "Boggart Shenanigans" for additional "Impact Tremors" and so on.
I would also use either some carddraw spells and/ or some 'pay {X}' spells to make sure you have something on your hand that you can make use of the amount of mana you have.

I'm not really a combo player, it's kind of frowned upon in our playgroup, so it's hard for me sometimes to recognise the interaction between the cards. With the description it's clear why you're keeping Tunneling Geopede.
"Mina and Denn, Wildborn", which you had in the deck before, would have been able to provide trample, but without any sort of evasion (and/ or removal) it's pretty useless, I totally agree on that.

Each decks should include a deck- and how to play description. The deck description should involve things as the basic idea why you did build this deck, if there's any story behind it, budget, certain cardchoices, especially if they deviate from common lists, legality, or any other information you can give others that will look at your deck. Best do this while you are building the deck because after some days important information's simply may not be remembered.
The how to play description is crucial for beginners. An experienced or expert builder can normally take a look at your deck and see how it should work, but there also are a lot of beginners out there that maybe want to take a look at this and compare it with their own ideas/ decks. Even for more or less standard-decks there should be a description just because of this.
By using deck-tags you can avoid to put unnecessary information into the deck name and thus making it too long. The tags also allows you to filter the decks you have made for a certain type, very useful if the number of decks you've build here steadily grows and grows.

When using cards like "Sakura-Tribe Scout"/ "Walking Atlas" ramp spells that allow you to play a land and search your library for an additional land become very strong, so "Kodama's Reach" could be a good card here.
Personally I would sideboard "Tunneling Geopede" for to something like "Plated Geopede"/ "Valakut Predator". Tunneling Geopede can be of use when playing against opponents with a strong defence that make it hard for you to come through.

Some more suggestions:
Adventuring Gear, Ghostly Flicker, Vines of Vastwood, Baloth Woodcrasher

Greetings
Muktol

Any particular reason why you're running so many 1-offs?

Well such Informations definitely belong onto the deck-description, just a deck-tag won't help much here. I would perhaps copy-paste the rules from the official site and also put a link of it up.

I would change some things here:
Lightning Strike -> Lightning Bolt ...cheaper and does the same thing.
Obelisk of Urd -> Quest for the Goblin Lord ...you don't have to tap creatures to cast this spell fast
Add 2 more mountains. 16 is a really low number especially when you have more cc2 and cc3 spells. A single land destruction spell can otherwise throw you complete off-balance.

As for the sideboard option of turning this into a burn deck, "Impact Tremors" can help you a lot here as well as "Raid Bombardment". Tremors benefits from your creatures entering while the Bombardment benefits from attacking creatures with power 2 or less.

Greetings
Muktol

+1
A card that works very good with "Quest for the Goblin Lord" would be "Mogg War Marshal", tough it might just be a little bit to slow here.
"Massive Raid" can be a very interesting card if you just cant get through your opponents defence.
"Legion Loyalist" provides you with trample and first strike for your goblin hordes.
"Searing Blood" could be removed for "Searing Blaze".

Personally I would trade 4 "Frenzied Goblin" for "Legion Loyalist", 2 "Lavastep Raider" for 2 additional "Raging Goblin". Sideboard "Pyroclasm" and "Smash to Smithereens" for e.g. "Massive Raid", "Goblin Grenade" or "Foundry Street Denizen".

Greetings
Muktol

I would use another enabler instead of "Memnite". "Invisible Stalker", "Tormented Soul", "Sage Owl" or "Faerie Impostor" are solid, modern legal, choices.
On the spell-side I'm personally using "Artful Dodge" and "Ghostform" to give my creatures unblockable. "Familiar's Ruse" gives you a little bit more control while it also allows you to play your ninjas again.
"Ronin Warclub" can help to boost you creatures damage a little bit.

Greetings
Muktol

"Great Furnance" is another good card to boost "Cranial Plating", as well as "Ancient Den". Only drawback is that they aren't modern legal and would be the only cards in this deck that would ruin your legality.
As they are only emergency cards "Mirran Crusader" and "Etched Champion" provide something that helps them to survive: Protection. The champion has the big advantage of having protection from all colours thus being unblockable by anything other than artifacts and unremovable by anything other than mass-exile, mass -x/-x or forcing you to sacrifice it. Only drawback is that you cant use "Assault Strobe" or "Magnetic Theft" on it.
"Steelshaper's Gift " may be something for the sideboard when you are forced to board a certain card to survive against an opponent and know that you will need in on the table very fast.

I would include a plan B if you Gaveleer gets removed. Personally I would splash white to get access to "Kor Duelist", "Mirran Crusader" or any other good, hard hitting, creature, best with some sort of protection/ evasion. "Etched Champion" could also be an option for this. Splashing would also give you access to things like "Dispatch" and "Steelshaper's Gift", furthermore some protective spells.

Some further suggestions:
Galvanic Blast; {R}; Instant; Deals 2 damage to target creature/ player, when metalcraft is active it deals 4 damage instead
Cranial Plating; {2}; Equipment; Equip {1}; Equipped creature gets +1/+0 for each artefact you control
Swiftfoot Boots; {2}; Equipment; {Equip {1}; Equipped creature has hexproof and haste
Darksteel Citadel; Artifact Land; Increases the artefact count for Cranial Plating

Greetings
Muktol

Each decks should include a deck- and how to play description. The deck description should involve things as the basic idea why you did build this deck, if there's any story behind it, budget, certain cardchoices, especially if they deviate from common lists, legality, or any other information you can give others that will look at your deck. Best do this while you are building the deck because after some days important information's simply may not be remembered.
The how to play description is crucial for beginners. An experienced or expert builder can normally take a look at your deck and see how it should work, but there also are a lot of beginners out there that maybe want to take a look at this and compare it with their own ideas/ decks. Even for more or less standard-decks there should be a description just because of this.
By using deck-tags you can avoid to put unnecessary information into the deck name and thus making it too long. The tags also allows you to filter the decks you have made for a certain type, very useful if the number of decks you've build here steadily grows and grows.

As for the deck, the first thing that came into my mind when thinking about zombies and devotion was "Geralf's Messenger". Triple {B}, hard to remove (undying) and deals damage when he enters the battlefield. "Skinrender" could be another option if you need more removal, while "Death Baron"/ "Cemetery Reaper"/ "Lord of the Undead" would boost your zombies.

Greetings
Moktol

The deck description could be a little more detailed. It can involve things as the basic idea why you did build this deck, if there's any story behind it, budget, certain cardchoices, especially if they deviate from common lists, legality, or any other information you can give others that will look at your deck. Best do this while you are building the deck because after some days important information's simply may not be remembered.
The how to play description is crucial for beginners. An experienced or expert builder can normally take a look at your deck and see how it should work, but there also are a lot of beginners out there that maybe want to take a look at this and compare it with their own ideas/ decks. Even for more or less standard-decks there should be a description just because of this.
By using deck-tags you can avoid to put unnecessary information into the deck name and thus making it too long. The tags also allows you to filter the decks you have made for a certain type, very useful if the number of decks you've build here steadily grows and grows.

As for the deck, I would beef up the mana-base a little bit as you have cards that have difficult mana-requirements, which might not be easy with only basic lands and Sandsteppe Citadel.
There are some other defenders that you also could consider, at last for the sideboard:
Axebane Guardian; {2}{G}; 0/3; Add X mana in any combination of colors to your mana pool, where X is the number of creatures with defender you control.
Order of the Stars; {W}; 0/1; As Order of the Stars comes into play, choose a color. Order of the Stars has protection from the chosen color.
Perimeter Captain; {W}; 0/4; Whenever a creature you control with defender blocks, you may gain 2 life.

I also would thing about another win-option because when "Assault Formation" gets removed, you basically only have "Archers' Parapet" left, which will take a long time. When using "Axebane Guradian" "Door to Nothingness" can be an option, "Helix Pinnacle" is also a (slow) way of winning in an deck with enough mana, or you include some big finisher, preferably with some sort of evasion (flying, unblockable, trample, and so on). Red and blue would feature defenders that burn/ mill depending on the number of defenders you control, but those would require a 4th colour splashed.

Greetings
Muktol

"Impact Tremors" could be an interesting card here, as well as "Goblin Bushwhacker".
Tremors help to deal damage (Mogg War Marshal = 3 damage, Akroan Crusader + Skin Invasion = 3 damage) while Bushwhacker helps with haste and a descent +1/+0 boost, and can be used as fodder for your other spells in case things go bad.

Why not splash black instead of white? Gives you access to a lot of control spells AND allows you the use of "Shaman of the Pack". Elvish Promenade, Dwynen's Elite, Eyeblight Massacre, Foul-Tongue Shriek would be interesting cards for this.

Personally I have run elves with the subtype warrior, but there might still be some good cards that fit into this deck:
Imperious Perfect; {2}{G}; 2/2; Other Elf creatures you control get +1/+1. {G}, {T}: Put a 1/1 green Elf Warrior creature token into play.
Nettle Sentinel; {G}; 2/2; Nettle Sentinel doesn't untap during your untap step. Whenever you play a green spell, you may untap Nettle Sentinel.
Talara's Battalion; {1}{G}; 4/3; Play Talara's Battalion only if you played another green spell this turn; Trample
Wren's Run Vanquisher; {1}{G}; 3/3; As an additional cost to play Wren's Run Vanquisher, reveal an Elf card from your hand or pay {3}. Deathtouch

Aside from that:
Collected Company; {3}{G}; Look at the top six cards of your library. Put up to two creature cards with converted mana cost 3 or less from among them onto the battlefield
Beastmaster Ascension; {2}{G}; WHenever a creature attacks it gets a counter. When five counters have been placed all your creatures get +5/+5

As for the splash, I would keep this monoG as it is now because white has nearly nothing that green can't do...if you're in for fast decks. White is the slower and more controlish colour here in my opinion.

Greetings
Muktol

Deck- and how to play description are missing.

Further suggestions:
Order of the Stars; {W}; 0/1; Defender; Protection from a chosen colour.
Axebane Guardian; {2}{G}; 0/3; Defender; Add X mana in any combination of colors to your mana pool, where X is the number of creatures with defender you control
Perimeter Captain; {W}; 0/4; Defender; Whenever a creature you control with defender blocks, you may gain 2 life

Basically when "Assault Formation" gets removed you're done, so why not add some additional finishers?
Door to Nothingness (needs Axebane Guardian), Helix Pinnacle, Entreat the Angels, Platinum Angel, Avacyn, Angel of Hope

Greetings
Muktol

I was thinking about "Merfolk Looter" (or "Mad Prophet") to more often activate Madness. But Menace could be an interesting option.
For now I will shuffle some card-numbers a little bit: -1 Artificer's Epiphany, -1 Cathartic Reunion, +2 Faithless Looting, -2 Looter il-Kor, +2 Insolent Neonate. I have also removed Sokenzan Spellbladeand added Pyre Hound instead.
When I had the chance to do some more testgames I will post how it went.

"Ensoul Artifact" also came back to my mind. Ensoul can convert your 0/2 Ornithopter into a massive 5/5 flying Ornithopter for just 2.
Searching for Ensoul Artifact and Ornithopter brought me to a very effective U/R deck with those cards in it. You can find an article from WotC under the following link:
http://magic.wizards.com/en/events/coverage/ptori/deck-tech-blue-red-ensoul-artifact-2015-08-01