Yes dear reader, you have read the title right. This deck is a Mono Green Mill deck. How does it work? I'm glad you asked.
First step is to get the "Mill" part first. Best bet is to get an Altar of the Brood out quickly. (opening hand is great. multiples are even better) but you don't want to play them all at once. I mean you can, but to get a stronger effect, Imprint them onto Prototype Portal and then you can make as many altars as possible. Notice how it says "any permanents" that can be land drops, artifact drops, creature drops, token drops, anything! So, while we are making a ton of altars we can spew out as many tokens as possible which then triggers the altar so the opponent has to mill. Even if you have 2 altars out and you play a Brood Monitor that's 8 cards milled just for casting a creature. AANNNDDD with the help of Conjurer's Closet we will be able to flicker creatures like brood monitor to mill yet another 8 cards! You maybe thinking this process can be slow, but let me tell you when you cast a Second Harvest and copy 10 tokens with 2 altars out, you will be a very happy camper... or player... whichever you want.
Another way to mill people is using
Sands of Delirium
along with Cryptolith Rite turning all of your tokens into even more mana (you tap a scion for any color, then sac it for a colorless means you get 2 mana per 1 token)
This deck can be flawed yes, but this is a strictly budget approach at a mono green mill deck :) This deck can be improved with much more efficient cards if you are willing to spend more $ on it. Thanks for taking the time to view this creation :) Feel free to leave a +1 on the deck!
If you want to spend a bit more money on the deck but dont want to break the bank, i suggest getting 2x Avenger of Zendikar as well as 2x Panharmonicon. both are roughly $5ish a card and are great additions to the deck. If you are wondering where to put them, I suggest taking out the 2x Birthing Hulk's as well as the 2x
Restock
for the 4 new additions to the deck. (Highly suggest getting the panharmonicons for great shenanighans) Thans again!