Nice deck! I have a few ideas for things.

I recommend running some card draw spells. Why? So you can fish for your win con (aka Assault Formation. Stuff like Sign in Blood, Read the Bones, Altar's Reap, etc.

Try going 11 Forests, 9 Swamps, that should balance out the wheel in the top right.

If you're going to add draw, I'd go for Read the Bones, two scry and draw is super powerful for 3 mana, and the life loss seems sustainable considering you have a buttload of defenders. If you decide to go for Sign in Blood instead, just go for Night's Whisper instead, since you're running a dual coloured deck, two black mana is harder to pull off than one black and one colourless, and you won't need the ability to target your opponent anyway.

As for the 60 card limit, basically the idea is that there's no point in adding any more cards than you have to, because even if that 61st card is amazing, if the other 60 are just a little bit more amazing, then why would you want a slight chance to draw a slightly worse card? The only instance where it is justified is if you have lots of scry and/or card draw, which you don't really have enough of here.

Right, I can try that. What would you suggest I remove to make room for Read the Bones?

Well, you have 5 Archers' Parapet, other than Relentless Rats and basic lands, you can only have 4 of one card in a deck, so take out one of those. Then, just take out as many Ornithopters as you want to get as many Read the Bones in as you want, up to 4 of course.

I actually only had 4 parapets in. I accidentally bumped it up by 1.

I also really dig the Ornithopter + Assault Formation combo here. It allows a 0/2 flyer for free that becomes a free 2/2 as soon as Assault Formation comes into play. I was considering taking out the single pump spells. Such as Mutagenic Growth and Ruthless Instincts considering that I have a play set of Vines of Vastwood.

Shape the Sands? Ukud Cobra has great value for this deck 5/5 deathtouch? i think yeah.

If you would be willing to splash white Doran, the Siege Tower is basicaly another Assault Formation.

also Skinshifter

I had a deck idea kind of like this where I used Doran, the Siege Tower and Rolling Stones as well. I ran mostly the ramp defenders and had Wall of Denial to swing huge or just killed them with Axebane Guardian + Banefire

Or Vent Sentinel

I love these wall defender decks! + from me!

kayin2000 oh man, I totally forgot about Rolling Stones! That would work wonders. And Doran, the Siege Tower seems like a great idea.

Bovine073 another total brain fart. Shape the Sands would be PERFECT here.

Thanks for the recommendations guys, I truly appreciate them.

Bovine073 I take that back, Shape the Sands is awesome but it only targets one creature. Tower Defense targets all of my creatures and does the same thing for just one more .

Axebane Guardian, Overgrown Battlement, and Sylvan Caryatid can give you some mana fixing while working towards your theme. Tree of Redemption can either get huge or heal you depending on the point in the game, and is definitely worth having a single copy of.

The version of this I play is Overgrown Colossus (Budget Modern).

Replace the mastodon with Tree of Redemption

+1 for the title before I even looked at the deck. Seems pretty good, how about Spidersilk Net for permanent buff and anti-flying? Avacyn is going to feel so bad when she gets eaten by a Sidisi's Faithful.

DaftVader yeah man I tried Spidersilk Net and it did pretty well. I may try to mainboard it in place of Anticipate since Vessel of Nascency is just strictly better for this deck.

Wouldn't Behind the Scenes make Sidisi's Faithful and Tide Drifter effectively unblockable?

Another enchantment for the deck: Tightening Coils. It helps mine.

Jaddi Offshoot seems like it would be a good sideboard card for this deck against agro

The new Tree of Perdition from Eldritch Moon might warrant an inclusion.