Couch312

True enough. It just sucks when Rabblemaster forces my other goblins to attack into Thalia or Deathrite.

Since it's casual you could run 4 Grindstone and 4 Painter's Servant just to have the option to infinite mill them if you need to.

Piledriver is better in most situations that Rabblemaster. 1 mana less, gets +2 for each other attacking goblin and doesn't make other goblins attack. However, Rabblemaster makes dudes and can win the game by itself, but the whole other goblins must attack is usually bad.

You should play battlefield thaumaturge as well, since if you have 4 creatures Assault only costs 2 red.

Top decking land is definitely a problem in mono red aggro. Throwing in 4 fetches would do a lot in thinning the deck to help you draw nothing but gas since 1 fetch thins the deck 2 lands.

I have to disagree with you.
The staples that carry over to legacy are the fetches. The only decks that transfer over are delver decks and burn, and even then burn gets Price of Progress, Chain Lightning and a couple other cards. Delver gets a million and one variants.
Brainstorm, Ponder, Preordain, Dark Depths, Deathrite Shaman, Stoneforge Mystic, Jace the Mind Sculptor, Dig Through Time, Glimpse of Nature, Green Sun Zenith, Punishing Fire, Divining Top, Punishing Fire, Umezawa's Jitte are all banned in modern.
Anything that is played in modern has a better version that is played in legacy. Serum Visions is a strictly worse preordain. Path to Exile is almost always worse than Swords to Plowshares. So on and so forth.
Snapcaster Mage, Vendilion Clique, Batterskull, Thoughtseize, Abrupt Decay, Tarmagoyf, Dark Confidant, and Liliana of the Veil are the only ones that carry over to legacy.

I understand that legacy is expensive to get into, but let's loo, at splinter twin in modern. Average cost of the deck non-foil, non-promo, alright condition cards is between 800 to 1000 dollars depending on the build. Bloom Titan being the most budgetish tier 1 deck in modern averages between 450 to 600 dollars. I mean, legacy is more expensive, but it's really not that much more expensive than Modern. You can build some pretty sweet decks for that kind of money. I play Mono Red Sneak attack in legacy, and it is ridiculously fun.

Also the part where you don't have to spend x amount of dollars every three months.

I would drop 2 Garruk and 4 Joraga Treespeaker and put 4 Burning Tree Emissary in and 2 Khalni Hydra. The reason I suggest these two is because turn 1 forest, mystic then turn 2 burning tree into burning tree into burning tree into play nykthos and use the two floating to tap it for 7 and lay down your hand is good. Also Khalni Hydra costs less the more you have.
I would also drop 4 Utopia Sprawls and add 2 Courser of Kruphix and 2 more lands. Modern mana ramp needs lands.
That's just my 2 cents, but I like green mana ramp and I like hard casting Emrakul, so +1.

Have you thought about Amulet of Vigor so your lands can enter untapped allowing you to actively cast things as you scapeshift? For instance, cast scapeshift, float whatever mana you have to in response to the sacrifice, grab a bunch of duals and valakut, all the U/R duals enter untapped so you can cast peer through the depths to try to find another scapeshift or something else to find more mountains, or just some burn spells to finish them off. So on and so forth.

I was wondering if I could get some advice on a modern mardu deck, not super competitive since I'm sure I just lose to Abzan value town or Splinter Twin, but I feel like it could be a tier 1.5 deck with some tweaking.

http://www.mtgvault.com/couch312/decks/modern-mardu/

Let me introduce you to Legacy Miracles. You don't win until turn 10 at the earliest assuming you entreat the angels for 1 on turn 3, but you lock your opponent out of the game so hard that your opponent just eventually gives up. Because Sensei's Divining Top and Counterbalance is disgusting.
There is also Death and Taxes, you don't win early, and you have game against everything. However, it is a deck that rewards competent play and shits on you if you only somewhat understand what you're supposed to do.
All variants of Stoneblade take much longer to win and also reward competent play since you have so many options and have to really have an in-depth understanding of the sequencing involved.
Then there is Burn which is back to tier 1 to 1.5 thanks to Eidolon of the Great Revel.
Variants of Delver.
The only decks that win on turn 1-3 are Storm, Elves, Dredge and Sneak and Show will occasionally win on turn 3. And let's be honest, dredge doesn't really play magic, it plays whatever sick game that is dredge.

Ever wonder why Serra Ascendant is 20 dollars? Commander, that's why.

Which reminds me, it actually runs careful study over Ponder because you want to be able to discard.

Not really, you run the full Brainstorm, Ponder, Probe and Force of Will. It also runs Reanimate, Entomb and Dark Ritual. Do you have a counter spell to stop animate dead? Do you have Swords to Plowshares in hand? And depending on the match it's sideboard is just straight reanimator. I.E Elesh Norn, Iona and whatnot.
It's as easy to stop as regular reanimator basically. Or storm depending on how the deck plays. Sometimes you just reanimate Griselbrand and draw 14 cards and go nuts with dark rituals and cabal rituals.

Yes, you cast animate dead targeting worldgorger, he comes into play and bounces animate dead which then puts him in the graveyard, and if you have no other legal targets for animate dead this happens forever since animate dead is not a choice once it enters the battlefield. Piranha marsh makes a target player lose 1 life, so if you have it in play Worldgorger bounces it forever until your opponent is dead.

Worldgorger can lock out the game turn 1 though if they turn 1 say a Deathrite. Worldgorger just goes, yep, can't win so we'll draw instead and go to game 2.

Fact. 2000 dollars once compared to 300-500 dollars every three months. I'll play legacy mkay thanks.

Worldgorger dat piranha marsh.

To be fair, lots of Legacy decks are interactive. The only decks that really don't are dredge and storm and even those have certain ways to interact. Sneak and Show probably has the least amount of interaction for being one of the more fair decks.
Also, Sneak and Show is shit on by one card, Containment Priest. Also Ensnaring Bridge. You can Oblivion Ring Emrakul, you can minus a Liliana or diabolic edict. The turn 1 Emrakul in sneak and show happens, but not nearly as often as you might think.
That said, I can understand how 60-70 dollars for a single card seems like a lot to spend for a casual player.

Expedition Map searches it out, and Crucible of Worlds helps keep it there in case it gets wasteland.