Muktol

I don't think that I will be needing Gyre Sage's ramp due to my rather low mana-curve. 2-3 Vorel of the Hull Clade would be an interesting option in a slower deck, but this deck tries to be rather fast (at last I hope so) and thus he might not be that strong.

The problem I see with normal fetchlands (Terramorphic Expanse, Evolving Wilds, and so on) is that the slow you down. The only way around that would be using the expensive ones (like Polluted Delta) but those are simply to expansive ($) to play in a deck built just for fun. Competitive tournament play is another thing.

Ghostly Flicker can even blink Shriekhorn to refresh it's counters and allow you to mill on, if nothing else is possible. So it's a very versatile card.

You may give your opponent another land. And this is not worth the 2 damage in my opinion. You thus also help him thin out his lands and draw key cards he might need.

So basically you want to 'convert' this into a modern burn/ Red Deck Win (RDW) deck.
I can't help you much on the creature side but on the spell side here are some suggestions:
Lightning Bolt ...cc1 for 3 damage to player or creature. There is no burn spell with a better damage/cost ratio.
Rift Bolt ...cc3; suspend with cc1. Takes a turn to make it's damage but else it's a 1:1 copy of Lightning Bolt.
Fiery Impulse ...cc1 for 2 damage. When you have 2 or more sorcery's/ instants in your graveyard it's 3 damage instead.
Searing Blaze ...cc2 for 1 damage to player and 1 damage to creature. When you had a land enter this turn it's 3 damage instead. Could replace Searing Blood
Dangerous Wager ...cc2, discard your hand and draw 2 cards. For this deck I would use it as sideboard option when you realize on game 1 that the following games might take longer.
Skullcrack ...cc2 for 3 damage and the player can't gain life this turn. A good sideboard option in my opinion but a waste against decks that don't use life-gaining spells or ability's.
Lava Spike ...cc1 for 3 damage to player. A spell also often played in burn/ RDW but the 'drawback' (in your case, you want to be able to target both creature and player to get rid of any blockers) is that it can only target the player.
Inferno Fist ...cc2; enchant creature. The enchanted creature gets +2/+0 and you can pay {R} and sacrifice the enchantment to shoot 2 damage to target player or creature
Assault Strobe ...cc1, target creature gains Double Strike.

Goblin Guide ...one of the 'standard' creatures in nearly each RDW. Cheap (cc1), powerful and fast but personally I dislike the drawback it has.

Greetings
Muktol

Just be aware that spells copied with Zada's ability won't count for storm-effects like "Empty the Warrens".
Also things like Guttersnipe won't trigger from it.

Greetings
Muktol

Your mana-curve is pretty low and with to much mana you'll have to rely on "Immerwolf" that your werewolf's don't get flipped back. With "Atarka's Command" you also already have something that could accelerate your play if needed.

My bad, completely forgot about the pauper bannlist.

Depends on the legality you want to build your deck for. I'm not good at building vintage/ legacy decks but modern I can help you with. Also the strategy you want to achive with your deck is important as there are new zombies that can convert a deck from beatdown to milling.

Some of the basic cards each deck can use:
"Cemetery Reaper" and "Diregraf Captain" are two more lords you could use. If it wouldn't be for the cc3 of their lords zombies could behave like Merfolk ^^
"Fleshbag Marauder" and "Skinrender" are walking removals that can go hitting your opponent after their work is done. "Tragic Slip" is one of the better new removals while "Bile Blight" can be a real deadly mass-removal
If you need some big creatures take a look at "Quest for the Gravelord".

Greetings
Muktol

I would trade 2 "Huntmaster of the Fells" for "Instigator Gang" as the Huntmaster has a little anti-synergy with "Immerwolf".
Also some additional protection like "Vines of Vastwood" or "Ranger's Guile" could be worth a look.

Greetings
Muktol

Any reason why you don't use "Invigorate"? If there is any better buff-spell for infect I don't know it.

Greetings
Muktol

Kaijin of the Vanishing Touch, Spectral Rider, Inquisitor's Flail, Apostle's Blessing and Skillful Lunge are some of the lower-cost spells I'm using in my own spirit deck.
(Serious Question, I'm building "normal" modern decks most of the time) Where's the difference between casual and non-casual?

For this kind of deck I would favour "Honor the Pure". "Intangible Virtue" sure is nice but the question is if the creature tokens are more important than the rest of your creatures. Also "Gideon Jura" (+0 ability) profits from "Honor the Pure" while he is unaffected by the Virtue.

Skullclamp is banned in modern.

The only problem I see with this deck is that it's mana-curve starts at cc3 and all your lands, save "Moorland Haunt", come into play tapped. So the chance that you can cast your first spell on T4 is pretty high. Until then you might have gotten some serious beatings and you opponent's hand will hold all the removal-spells he has drawn.

Greetings
Muktol

This reminds me a lot on the beginnings of first deck, though it may look different now. *like*(http://www.mtgvault.com/muktol/decks/monow-tribal-human-wheeny/)

"Kazandu Blademaster" instead of "Elite Inquisitor" gives you the chance of getting the Blademaster to 3/3 or even 4/4 and the only thing you would loose is protection from vampires, werewolves and zombies.
"Riders of Gavony" can be put into your sideboard simply because not every deck you will have to battle will have a strong tribal theme.
"Mentor of the Meek" is a carddraw-engine especially when one or two "Thraben Doomsayer" are on the field.
I would perhaps replace "Commander's Authority" with "Goldnight Commander" or do a 2/2 split between them. The problem with the Authority is it's an enchantment (if the creature gets removed you loose both cards), it's expensive to play and it's slow. If you would get 2-4 tokens per turn that would be OK but for only one token this enchantment doesn't do enough.
I would also look for some removals and/ or protection (my own deck uses "Emerge Unscathed" and "Path to Exile") to be able to deal with threads your opponent puts before you.

Greetings
Muktol

I would change the creature base dramatically: "Blight Mamba", "Ichorclaw Myr" and "Signal Pest" are better choices for such decks. You don't need the mana-elves as you simply don't have any 'pay X' spell in your deck or any other spell that would require much mana.
As for "Invigorate" replacements there are some: "Evolution Charm", "Ranger's Guile", "Vines of Vastwood", "Rancor". If you are willing to play cc3 enchantments take a look at "Wild Defiance"

25 land will definitely be on the high side for such decks 20 should be enough.

Greetings
Muktol

Some deck-description would be nice. Color combination, budget, strategy, legality, and so on.
Like many tribals zombies can be played in various ways: Aggro, control, mill are 3 that came to my mind in an instant.

Greetings
Muktol

I mean no offense but you might want to read http://www.mtgvault.com/muktol/decks/how-to-build-a-deck/
Short version: There are way to many different cards in here to make this an effective deck.
Also a short deck description (strategy, budget, why did you built it, and so on) and a how to play (for all of the decks you have and you will built here) would be nice.

Greetings
Muktol

*like*
"Precursor Golem" is a good card, the only problem with him is that you have no way to protect him without loosing each golem on the field (save the two you get back when you blink him).
My own version (http://www.mtgvault.com/muktol/decks/gwu-golem-tokens/) plays some green hexproof spell's like "Ranger's Guile" or "Vines of Vastwood".
Also if you're playing "Cloudshift" and "Momentary Blink" you might want to take a look at "Ghostly Flicker". Great card that blinks you two creatures/ artifacts or lands in one spell.
you might also want to give "Tempered Steel" a second thought. The weak point on this deck are the splicer's itself, not the golems. So "Adaptive Automaton" or something similar (+1/+1 for humans) might be a better idea.

Greetings
Muktol

Some suggestions based on my own monoR Krenko commander deck (http://www.mtgvault.com/muktol/decks/edh-krenko-mob-boss/)
Bloodmark Mentor, Furystoke Giant, Goblin Assassin, Goblin Bushwhacker, Goblin Wardriver, Battle Squadron
Ruination, Mob Justice, Chaos Warp, Dangerous Wager
Champion's Helm, Konda's Banner, Magewright's Stone, Thornbite Staff, Thousand-Year Elixir
Quest for the Goblin Lord, Shared Animosity

Greetings
Muktol