Welcome to my database of cards in my stream of thought mill
You can see all the cards I've described by searching for the tag: wdm mill guide
The cards in the sideboard are covered in this article and you can see the cards while you read how I use them.
When I want to see if mill is doing well in modern, all I look at is surgical extraction and extirpate. In easy times there will be most surgical while at hard times extirpate dominates. Why is this a good measure ? Well, surgical extraction is one of the oldest tricks in mill to deny an opponent with, you can remove four keycards with one card. In mills latest heyday this could be seen by mill playing 4 surgical extraction and 4 snapcaster mage, which was the key to mills victories. A single card would put a stop to this. Relic of progenitus. When mill tried to target a keycard in the opponents graveyard with a surgical extraction, the relic player could simply use relic to exile that specific card, which would make the surgical fizzle. Worse, a player with multiple relics could also prevent a miller from using snapcaster to recast their best mill by slowly removing all the good mill, or removing it all in cases of emergency. Ever since it's printing relic have stood guard against mill until a couple of month's ago where it was abandoned by modern players for a reason, and mill simply resurged, quickly conquering 5% of the meta with 3 different mill types. Relic of progenitus defines mill. Once it was gone mill also started to use snapcaster mage again, which had been out of successfull mill lists for at least 5 years.
The easiest way to exploit surgical extraction is to gain access to it at your turn 1, through cards that mill a small amount, like thought scour, stream of thought or merfolk secretkeeper// venture deeper. One of my all time favourites are chancellor of the Spires, that can be used during your opponents upkeep before the game has really started. If you don't dig out a keycard at turn one you continue the search at turn two with cards like glimpse the unthinkable or breaking // entering.
When you face a player with few lands and multiple colors, you can play it dirty by targeting their lands with your surgical extractions target their fetchlands first as they get to decide what lands they get with fetchlands, then target any dual lands that would improve their manabase. This trick also makes mind funeral work as on steroids. I've won games by taking out two different duals at turn 1, some players simply concede and starts shuffling for the next game.
Snapcaster mage is brilliant with this card, but over the years mill was tried to be improved upon by designers who didn't understand the relic problem. Mission briefing is one of the better attempts they catch the concept that millers want to recast their good mill. Later they designed watchers of tomorrow which emulates snapcaster better under games against relic but still doesn't solve the whole problem. It's still good but millers haven't discovered the card yet. There is also "the grand old man" augur of bolas whom the mob of millers never got right. Back then I was running daily analysis on mill and discovered that snapcaster mage won all the small local tournaments, while augur of bolas won all the major 100+ people tournaments. At larger tournaments aggro is much more dominant so augur of bolas shines in that environment, especially times when relic of progenitus is present. I've been stating this for years, waiting for millers to spread this word, but millers in general don't reveal their tricks.
I also use noxious revival to regain surgical extraction and had great success with a version with surgical extraction, snapcaster mage and noxious revival in the same mill deck once, where my goal was to target the manabase.