Have you consider ash zealot instead of rakdos shred-freak. It's a bit of a strain on the mana base being double red, but it's a 2/2 haste for 2 with first strike. It also has a an effect that hates out snapcaster mage. "whenever a player casts a spell from his/her graveyard ash zealot does 3 damage to him/her" or something along those lines. There's also ashenmoor gouger if you like 4/4s for 3 mana. Not even an issue with the mana base because it's a black/red hybrid. Only downside is it can't block so it's definitely a card you play when you're banking everything on pure aggression. I can't tell if you're trying to keep it within a specific budget or not but goblin is generally speaking a must play card for these kinds of decks. A 1 mana 2/2 haste is worth the downside of maybe drawing your opponent a card.
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silly mexican you don't have fun
needs painful quandary
add doom blade to the sideboard for artifact decks. love the fact that it kills the blightsteel centered decks with the discard.
Add grasp of darkness for the very few creatures which are indestructible.
why do you have birds of paradise? an infect deck should not have to mana ramp. if you are going to make the deck tricolored add a few non basic lands.
the most annoying mill deck on Earth. Have fun against burn decks. :)
use swords to plow shares maybe instead of unmake. unmake might cost a little too much especially if you are facing a fast deck like a goblin deck.
add oracle of muldaya
add negate for day of judgement.
watch out for infect
add darksteel or blightsteel collosus just in case someone tries a day of judgement.