wickeddarkman

Looks like a very well thought out design.
It's the best hybrid between UB and esper mill that I have seen so far.

A few details stick out though:

With aggro having a 51% presence in modern and both combo and control having lots of creatures, what is your general basis for placing path to exile in the sideboard?

Is leyline of sanctity really necessary? It's probably there against combo, but wont surgical and extirpate handle that?

Isn't ratchet bomb too slow and too narrow to have a real good effect?

Based on my own milling experiences against affinity,elves, infect and merfolk, I can recommend that you replace 1 archive trap and replace it with a single mesmeric orb. (My own deck features 1 trap and 1 mesmeric orb) Most pro's don't use their fetchlands once they discover that you play mill.
http://www.mtgvault.com/wickeddarkman/decks/the-story-so-far/

What's the best and worst matchups?

Unless you have something that taps lands, chronic flooding won't fool a pro as they will play around it.
If you use it to selfmill with, it's actually a nice idea and I can recommend dream twist as well.
However, mesmeric orb is a much better pick at either purpose.

Perhaps ancient stirrings to get painter faster?

THE "SHRIEKHORN IS BETTER THAN TOME SCOUR" CAMPAIGN:

First of all, it's colorless, so if you are stranded with a swamp at turn 1, you can get going with shriekhorn already that turn.

I've been playing with both tomescour and shriekhorn in my modernmill, and for more than 200 games I have been registering how much shriekhorn mills on an average. The basis is that I play 4 and play them within a priority to keep track of what happens to lategame shriekhorns, so the first numeric results are always for the most played shriekhorn, while the last is for the least played shriekhorn (which sometimes doesn't get played)

I've tested against the fastest decks on the field (Well elves are not that fast, but I tested it anyways)

SHRIEKHORN VS MERFOLK:
5.571, 5.333, 5.142, 5.037
At no point it drops below 5, so it is statistically better than tomescour.

SHRIEKHORN VS AFFINITY:
5.538, 5.2, 4.888, 4.5
Half of the shriekhorns drop below 5 so two could be replaced with tomescour.
SHRIEKHORN VS INFECT:
5.111, 5, 5, 4.5
They still stay above 4 so no exchanges.

SHRIEKHORN VS ELVES:
5.5, 5.5, 5, 4.888
One drops below 5 and could be replaced.

BUT WHAT ABOUT DECKS WITH ARTIFACT HATRED ???
First of all, only a few nuts persons would target a shriekhorn to destroy it, and in general if they really really want to target your horn, then let them and play mesmeric orb or other superior artifact mill.

SHRIEKHORN HAS OTHER USES:
In legacy I've often used shriekhorn to disrupt cards set for counterbalance, but there must be modern decks where instantly disrupting the top of a library counts for something.
Also, a lot of players favor echoing truth as a sideboard card in modern, and by echoing shriekhorn you gain a fresh mill-clock.

First instance of the card says "Each player shuffles his or her hand AND LIBRARY" So whatever you normally milled from any player is reshuffled, time wasted on milling!

On the tutelage/day interaction the mill-ruling states that a player needs to draw a card to die, so putting cards away isn't lethal. I'd have to guess that the first parts of day first reshuffles decks, then 7 triggers stack on tutelage, then day ends the turn and remove the stack so cards never get milled anyway's. However I'm not good at layers and that stuff so if anyone more guru says otherwise I'll find the strategy fun enough :D Any way I can see the idea now.

713.1
This new rule explains a bit more about Day's Undoing and ending the turn. Day's Undoing is the first card that has additional effects before it ends the turn. If any abilities trigger while players are shuffling or drawing cards, before the "end the turn" procedure starts, those abilities won't be put onto the stack. The "end the turn" procedure will essentially eat them. Of course, abilities that trigger during the "end the turn" procedure will go on the stack during that turn's cleanup step. (These abilities are pretty rare though.)

So after all this, I agree that day can be used in a deck that mills, but not in ordinary mill.

It's your mana!
It takes 25 lands to support hardcasting any 5cc at turn 5 reliably.
It takes 22 lands to cast something reliably at a cost of 3cc.
So casting something costing 4cc will demand 23-24 lands.

shriekhorn beats tome scour statistically. (I've done the research with 200+ games)

Somethings wrong with the legality of the deck.
It has treasure cruise which is banned in modern.

Also I've pointed out to another that when you play mill, you don't want to play day's undoing

You'd also gain ancient stirrings for the bridge. Green also has a lot of "selfmill" and selfmill creatures like ghoultree and gurmag angler.

Here's my take on a mill deck with ensnaring bridge:
http://www.mtgvault.com/wickeddarkman/decks/wicked-bridgemill/

This is highly experimental, so I'll add some experimental stuff.
Simian spirit guide and nykthos can provide red mana, so splash in some red/black lands as well and you can make the deck R/B, which allows for several things. (Pyroclasm)

Fulminator mage is wellknown for it's use against tron, so try it out alongside ghostquarter for more landdestruction.

Your main problem will be generating lots of mana and creatures for your balustrade/undercity theme, so consider adding the final 2 nykthos with that in mind, and also consider æthervial.

Trust me on the chancellor, it's worth the drawbacks if you want to lock down other decks fast. Try out three, put paperslips in their sleeves, and note everytime they mill, and every time they are drawn at a bad time. You will soon find that they help more than they hinder :D You may also consider trying them out with shelldock isle which can play them.

I also try to think both longterm and "right now" choices, which is why I play such stuff as chancellors and shriekhorns. I spend months trying to finetune my mill :D

If you really want to go for their land you will need more than just 4 cards to support surgical extraction.
I use 4 tome scour, 4 shriekhorn, 3 memory sluice and 3 chancellors of the spires to fully exploit surgical extraction.

You could also be using memory sluice, shriekhorn and ghost quarters as a "land hate"-strategy. I've seen at least one deck trying this approach:
http://www.mtgvault.com/kjsj3/decks/millin-krillin-v2/

THE "SHRIEKHORN IS BETTER THAN TOME SCOUR" CAMPAIGN:

First of all, it's colorless, so if you are stranded with a swamp at turn 1, you can get going with shriekhorn already that turn.

I've been playing with both tomescour and shriekhorn in my modernmill, and for more than 200 games I have been registering how much shriekhorn mills on an average. The basis is that I play 4 and play them within a priority to keep track of what happens to lategame shriekhorns, so the first numeric results are always for the most played shriekhorn, while the last is for the least played shriekhorn (which sometimes doesn't get played)

I've tested against the fastest decks on the field (Well elves are not that fast, but I tested it anyways)

SHRIEKHORN VS MERFOLK:
5.571, 5.333, 5.142, 5.037
At no point it drops below 5, so it is statistically better than tomescour.

SHRIEKHORN VS AFFINITY:
5.538, 5.2, 4.888, 4.5
Half of the shriekhorns drop below 5 so two could be replaced with tomescour.
SHRIEKHORN VS INFECT:
5.111, 5, 5, 4.5
They still stay above 4 so no exchanges.

SHRIEKHORN VS ELVES:
5.5, 5.5, 5, 4.888
One drops below 5 and could be replaced.

BUT WHAT ABOUT DECKS WITH ARTIFACT HATRED ???
First of all, only a few nuts persons would target a shriekhorn to destroy it, and in general if they really really want to target your horn, then let them and play mesmeric orb or other superior artifact mill.

SHRIEKHORN HAS OTHER USES:
In legacy I've often used shriekhorn to disrupt cards set for counterbalance, but there must be modern decks where instantly disrupting the top of a library counts for something. (tutor-stopping?)
Also, a lot of players favor echoing truth as a sideboard card in modern, and by echoing shriekhorn you gain a fresh mill-clock.

THE "SHRIEKHORN IS BETTER THAN TOME SCOUR" CAMPAIGN:

First of all, it's colorless, so if you are stranded with a swamp at turn 1, you can get going with shriekhorn already that turn.

I've been playing with both tomescour and shriekhorn in my modernmill, and for more than 200 games I have been registering how much shriekhorn mills on an average. The basis is that I play 4 and play them within a priority to keep track of what happens to lategame shriekhorns, so the first numeric results are always for the most played shriekhorn, while the last is for the least played shriekhorn (which sometimes doesn't get played)

I've tested against the fastest decks on the field (Well elves are not that fast, but I tested it anyways)

SHRIEKHORN VS MERFOLK:
5.571, 5.333, 5.142, 5.037
At no point it drops below 5, so it is statistically better than tomescour.

SHRIEKHORN VS AFFINITY:
5.538, 5.2, 4.888, 4.5
Half of the shriekhorns drop below 5 so two could be replaced with tomescour.
SHRIEKHORN VS INFECT:
5.111, 5, 5, 4.5
They still stay above 4 so no exchanges.

SHRIEKHORN VS ELVES:
5.5, 5.5, 5, 4.888
One drops below 5 and could be replaced.

BUT WHAT ABOUT DECKS WITH ARTIFACT HATRED ???
First of all, only a few nuts persons would target a shriekhorn to destroy it, and in general if they really really want to target your horn, then let them and play mesmeric orb or other superior artifact mill.

SHRIEKHORN HAS OTHER USES:
In legacy I've often used shriekhorn to disrupt cards set for counterbalance, but there must be modern decks where instantly disrupting the top of a library counts for something.
Also, a lot of players favor echoing truth as a sideboard card in modern, and by echoing shriekhorn you gain a fresh mill-clock.

I'll give you the advanced "shriekhorn is above tome scour" campaign!
First of, all my research (more than 200 games) with my own milldeck have given me the statistics of how much shriekhorn actually mills, and it is superior to tomescour in many ways, (Colorless, can disrupt "on the top"-tutors, mills more)

In your deck it will perhaps enable you to play with one more ghost quarter if you remove another land (maybe even two)

I also think you should try to go "full scale" with ensnaring bridge. Run 4 ensaring bridge, 4surgical extractions and 4 extirpate which will take care of combo, and which will be able to remove any artifact hatred that you encounter in aggro.

To speed up emptying your hand you may as well consider playing 4 street wraith or 4 faerie macabre or even 4 simian spirit guide.

YAY!

You play shriekhorn, so consider echoing truth in your sideboard :D

THE "SHRIEKHORN IS BETTER THAN TOME SCOUR" CAMPAIGN:

First of all, it's colorless, so if you are stranded with a swamp at turn 1, you can get going with shriekhorn already that turn.

I've been playing with both tomescour and shriekhorn in my modernmill, and for more than 200 games I have been registering how much shriekhorn mills on an average. The basis is that I play 4 and play them within a priority to keep track of what happens to lategame shriekhorns, so the first numeric results are always for the most played shriekhorn, while the last is for the least played shriekhorn (which sometimes doesn't get played)

I've tested against the fastest decks on the field (Well elves are not that fast, but I tested it anyways)

SHRIEKHORN VS MERFOLK:
5.571, 5.333, 5.142, 5.037
At no point it drops below 5, so it is statistically better than tomescour.

SHRIEKHORN VS AFFINITY:
5.538, 5.2, 4.888, 4.5
Half of the shriekhorns drop below 5 so two could be replaced with tomescour.
SHRIEKHORN VS INFECT:
5.111, 5, 5, 4.5
They still stay above 4 so no exchanges.

SHRIEKHORN VS ELVES:
5.5, 5.5, 5, 4.888
One drops below 5 and could be replaced.

BUT WHAT ABOUT DECKS WITH ARTIFACT HATRED ???
First of all, only a few nuts persons would target a shriekhorn to destroy it, and in general if they really really want to target your horn, then let them and play mesmeric orb or other superior artifact mill.

SHRIEKHORN HAS OTHER USES:
In legacy I've often used shriekhorn to disrupt cards set for counterbalance, but there must be modern decks where instantly disrupting the top of a library counts for something.
Also, a lot of players favor echoing truth as a sideboard card in modern, and by echoing shriekhorn you gain a fresh mill-clock.

THE "SHRIEKHORN IS BETTER THAN TOME SCOUR" CAMPAIGN:

First of all, it's colorless, so if you are stranded with a swamp at turn 1, you can get going with shriekhorn already that turn.

I've been playing with both tomescour and shriekhorn in my modernmill, and for more than 200 games I have been registering how much shriekhorn mills on an average. The basis is that I play 4 and play them within a priority to keep track of what happens to lategame shriekhorns, so the first numeric results are always for the most played shriekhorn, while the last is for the least played shriekhorn (which sometimes doesn't get played)

I've tested against the fastest decks on the field (Well elves are not that fast, but I tested it anyways)

SHRIEKHORN VS MERFOLK:
5.571, 5.333, 5.142, 5.037
At no point it drops below 5, so it is statistically better than tomescour.

SHRIEKHORN VS AFFINITY:
5.538, 5.2, 4.888, 4.5
Half of the shriekhorns drop below 5 so two could be replaced with tomescour.
SHRIEKHORN VS INFECT:
5.111, 5, 5, 4.5
They still stay above 4 so no exchanges.

SHRIEKHORN VS ELVES:
5.5, 5.5, 5, 4.888
One drops below 5 and could be replaced.

BUT WHAT ABOUT DECKS WITH ARTIFACT HATRED ???
First of all, only a few nuts persons would target a shriekhorn to destroy it, and in general if they really really want to target your horn, then let them and play mesmeric orb or other superior artifact mill.

SHRIEKHORN HAS OTHER USES:
In legacy I've often used shriekhorn to disrupt cards set for counterbalance, but there must be modern decks where instantly disrupting the top of a library counts for something.
Also, a lot of players favor echoing truth as a sideboard card in modern, and by echoing shriekhorn you gain a fresh mill-clock.

THE "SHRIEKHORN IS BETTER THAN TOME SCOUR" CAMPAIGN:

First of all, it's colorless, so if you are stranded with a swamp at turn 1, you can get going with shriekhorn already that turn.

I've been playing with both tomescour and shriekhorn in my modernmill, and for more than 200 games I have been registering how much shriekhorn mills on an average. The basis is that I play 4 and play them within a priority to keep track of what happens to lategame shriekhorns, so the first numeric results are always for the most played shriekhorn, while the last is for the least played shriekhorn (which sometimes doesn't get played)

I've tested against the fastest decks on the field (Well elves are not that fast, but I tested it anyways)

SHRIEKHORN VS MERFOLK:
5.571, 5.333, 5.142, 5.037
At no point it drops below 5, so it is statistically better than tomescour.

SHRIEKHORN VS AFFINITY:
5.538, 5.2, 4.888, 4.5
Half of the shriekhorns drop below 5 so two could be replaced with tomescour.
SHRIEKHORN VS INFECT:
5.111, 5, 5, 4.5
They still stay above 4 so no exchanges.

SHRIEKHORN VS ELVES:
5.5, 5.5, 5, 4.888
One drops below 5 and could be replaced.

BUT WHAT ABOUT DECKS WITH ARTIFACT HATRED ???
First of all, only a few nuts persons would target a shriekhorn to destroy it, and in general if they really really want to target your horn, then let them and play mesmeric orb or other superior artifact mill.

SHRIEKHORN HAS OTHER USES:
In legacy I've often used shriekhorn to disrupt cards set for counterbalance, but there must be modern decks where instantly disrupting the top of a library counts for something.
Also, a lot of players favor echoing truth as a sideboard card in modern, and by echoing shriekhorn you gain a fresh mill-clock.