DedWards

I find that gatherer is very useful, you just need to use the correct key words and filters. What annoys me about it is I often forget to use American spelling for some of the words, so I sometimes don't get a result. Another thing I've found helpful is reading comments on the cards, I've found some interesting combos from the comments.

Both Midnight Guard + Presence of Gond and Devoted Druid + Quillspike combos in one deck? Interesting... Might I suggest trying to include some Sigil of the Nayan Gods? It allows Devoted Druid to substitute for Midnight Guard and if on another creature when you do combo for infinite tokens, it allows you to have a huge creature attacking the turn you combo.

Thornbite Staff + Marrow-Gnawer + {any other rat} = infinite rat tokens.

Sharding Sphinx can help get the fuel for Time Sieve.
Etherium Sculptor can lessen the recasting of Thopter Assembly.

I only mentioned Mutilate as it's a big card in my Heartless Summoning deck that I've been playing a lot recently. Massacre Wurm is another big one in the deck. It wipes out small creatures and combos well with Mutilate :P

Zealous Conscripts, though 5 mana, is a red creature that works with Splinter Twin / Kiki-Jiki.

I'm only commenting to answer your question of "Can you figure out a way to beat this?" My answer is Mutilate :P

Stoke the Flames works nicely with Jeskai Ascendancy's untap effect

Berserk is the one card stopping this deck from being Modern legal. I have a few suggestions that will both make this Modern legal and remove the need for green:

Artful Dodge in place of Distortion Strike - gives you more control over the second use of the unblockable effect and lets you cast it twice in one turn.
I'm assuming Flesh // Blood is in here for the Fling effec, so Soul's Fire could fill that role role.
Berserk and Temur Battle Rage have a similar end effect on an attack. Sadly it doesn't boost for Fling effects. Alternatively, Fatal Frenzy works exactly like Berserk, only for more mana :|
Giant Growth and Brute Force are identical, just one is green while the other is red.
Lastly, instead of Elvish Mystic, I'd include some Apostle's Blessing. It may not provide mana, but it serves a different role of protecting the creature from opopponent's removal (also works as a way to grant a pseudo 'unblockable' effect).

These possible changes keeps most of what you did here intact.

That's a very good sideboard option. Was kind of thinking of Weapon Surge to do the same thing. Both have pros and cons...

All good card, but not quite what I'm going for here.
Anax and Cymede, Phalanx Leader, and Iroas, God of Victory work best with multiple creatures.
Ordeal of Helliod and Ordeal of Purphoros, while good cards, aren't instants. And protection could cause them to fall off before their effects can go off.
Defiant Strike does doesn't do much apart from drawing me only 1 card. I prefer Mortal's Ardor for the lifelink.

My goal is to beef up one, maybe two creatures at instant speed, while leaving enough mana open for the protection spells.

18 fogs, 8 of which cost 1 mana, with 4 Elixirs returning them to my library (and gaining 5 life), and your suggestion of the Ghostly Prisons should be more than enough to not require chump blocking. In most other deck types, I'd probably use the Familiar over Tithe.

Aegis of the Gods is a cool alternative to Leyline of Sanctity, thanks :)
I personally prefer Mana Tithe over Judge's Familiar because it doesn't advertise that I can counter, but it does make for good redundancy (Tithes 5 to 7).
Sadly, Test of Faith can only prevent damage to a creature...

I feel that I should point out that Dawn Charm can counter a spell targeting me, thus making for a small amount of protection against burn.

Nice. I also looked up state based actions in the comprehensive rules and one rule's (704.4) example is this:

A player controls a creature with the ability "This creature’s power and toughness are each equal to the number of cards in your hand” and casts a spell whose effect is "Discard your hand, then draw seven cards." The creature will temporarily have toughness 0 in the middle of the spell’s resolution but will be back up to toughness 7 when the spell finishes resolving. Thus the creature will survive when state-based actions are checked. In contrast, an ability that triggers when the player has no cards in hand goes on the stack after the spell resolves, because its trigger event happened during resolution.

So I guess I was worried about my friend's Puzzle Box for nothing :p

I actually have a set of promo foil Kor Firewalkers, was wanting to use them in a Pyrohemia deck, but I guess they make cool sideboard option here.

Leyline of Sanctity would probably be the best answer, but +- $30 per card is a bit much...

How about Mana Tithe?

I've been running a GW heroic deck for the last few months and I've found it best to have cheaper (mana) creatures, about 16 to 18 creatures, with a sizable protection package, about 16 protection / indestructible instants, and a set of an instant that grants lifelink (Mortal's Ardor). You don't seem to be using the best 1 drop white heroic creature: Favored Hoplite.

Here's what I would use as a base for a Boros Heroic deck:
http://www.mtgvault.com/dedwards/decks/boros-needs-a-hero/
Maybe you could get an idea or two from it?

Sprinting Warbrute's dash costs 4 mana. Sure, it's a beefier creature, but I want to keep the dash cost low, in case I don't have any Warbringers. I'm going for more of a cheap speed effect.

Brutal Hordechief doesn‘t even have dash (though it has cool ability) and it's a mythic rare. I don't intend on spending money on cards for a while as I'm hoping Battle for Zendikar to have some cool stuff, including full art basic lands, so I want to save up for when Battle for Zendikar comes out.

Sadly, I don't have all the cards to test this deck, and without getting a feel for this deck, I doubt I can be much help with your deck.

Rofellos can supply a lot of mana, so have you thought about adding Hurricane and Squall Line? I doubt people will expect X damage coming out of mono green :p

Other Slivers that may interest you:
Sidewinder Sliver
Virulent Sliver
Sinew Sliver
Harmonic Sliver (for sideboard)
Essence Sliver


Also, some instant speed protection / hexproof couldn't hurt. I use Vines of Vastwood mainbord and Autumn's Veil or Avoid Fate in the sideboard.
Rancor is awesome in any aggro deck that has access to green.