Contested War Zone - Gives you more explosive starts. This deck lives and breathes mass pump, so you'll want these.
Teetering Peaks - Played in certain red decks. Usually too slow in KRed, but test it out for yourself.
Memnite - It gives you an additional creature on turn one, which is crucial. You want to swing with a pumped up team on turn 2 - at the latest - and an extra 1/1 is well worth the card it costs.
Signal Pest - Another one of your bread-and-butter cards. Again, mass pump is why this deck works, so play these.
Goblin Bushwhacker - Another must-play card.
Ornithopter - If you want extra free guys. Also, it flies.
Myr Sire - Doesn't die to sweeps. Costs 2 mana, though.
Hero of the Oxid Ridge An endgame threat, if you feel that you need it. Costs 4 mana, though.
Spikeshot Elder - A powerful red 1-drop. Often considered too slow here. Test it out yourself.
Devestating Summons - Another card to make multiple creatures. Risky - most people don't play four.
Lightning Bolt - Remove blockers or three to the face. Moving on.
Searing Blaze - Removes a blocker and deals three to the face. At the same time. o_O
Mox Opal - Lets you empty your hand quicker, while still having mana open to kick Bushwhacker. Very good here.
Chimeric Mass - A creature which doesn't die to sweepers (other than Ratchet Bomb set to 0).
Koth of the Hammer Gives you an endgame threat, if you feel that you need it. Again, mana cost can be a problem.
Manic Vandal/Crush/Shatter - Kills artifacts dead. Shatter is probably the best one here, though, as Vandal is slow and Crush doesn't kill Wurmcoil Engines, animated artifacts and other artifact creatures.
Also, whichever one of Searing Blaze and Arc Trail you aren't running MD should probably go here - you often don't want to play four of both in the main deck, but whichever you choose (either/or or a split) you often want access to the other one(s).