Monoblack infect deck ridiculously simple and fun to play: just wipe out with Dismember, Slaughter Pact and Go for the Throat, even Damnation if things get ugly. You can eliminate almost any creature with these 4 types of removal. Thoughtseize is used to get rid of key pieces of your rival's deck that aren't creatures.
Inkmoth Nexus, Plague Stinger and Ichorclaw Myr will hit without opposition (if there were any annoying blockers, just kill them all).
If the creatures mentioned above are in trouble, Phyrexian Crusader is your second line infantry. He will laugh at all those Lightning Bolt and Path to Exile that most people like, and will pass through the typical flying white spirits with absolute impunity. Also, Phyrexian Vatmother and Skithiryx, the Blight Dragon are absurdly strong creatures that can finish your opponent in one or two blows, specially useful in the mid-late game.
Hand of the Praetors and Mutagenic Growth boost your poisonous creatures so they can bring Phyresis to your opponent faster.
Finally, Phyrexian Arena refills your hand so that the opponent cannot take advantage on you.
The deck, which is quite cheap, proved to be competitive against several 700-800$ decks like Junk Midrange, Esper Control/tokens, W/U Exalted and others. Still loses against the typical 1000-1500$ absolute control decks with Snapcaster Mage and all the stuff. I have to play it more and more to know its weak points.
I would be very grateful if anyone could help me to build the sideboard since I haven't decided what to run yet. Thank you for your help and don't forget to comment and suggest if you like the deck!