Your deck has 4x Vapor Snag.. you can't even make sure you have a bounce spell in your opening hand. Cards like Elite Vanguard are going to punish the hell out of you. Then.. you're going to want to tap out on turn 3 to play discards, now your counterspells are offline.. now an opponent can slip through a Goblin Rabblemaster, Rhox War Monk or some.other.horrid 3 drop. I really think, if you want to play discard, going with removal is a better option than going with counters IMO. Dead Weight, Shadowborn, and a few Flesh to Dust.. and most importantly, creatures that can block. Guard Gomazoa was huge for.me in my discard build.. and so was Phyrexian Rager as they can both block.
Dead Weight, totally overlooked this card, at 1 black mana cost (-2/-2) I see it working really well (will incorporate with your other suggestions). Surprisingly, a lot of decks do not run Elite Vanguard, or if they do, that creature is usually pumped up with Auras by turn 2/3, thus making it more valuable to send back to the owner's hand. Nevertheless, it and cards like it have delivered a great deal of damage when not addressed soon enough.
With respects to Goblin Rabblemaster (this is a very popular card) and other three mana nightmare drops, I plan to have enough interrupt type spells to take care of it (and not to leave myself closed out to discard) at turn three. If closed, should have a kickback spell, then interrupt the next turn, and followed by another discard, and so on.
Brain Maggot, what a gem that card is early on. I can see the other player's hand and then coordinate.
Not to sure about Shawdowborn or Flesh to Dust, they are a bit expensive, will consider and see how these cards work.