My post generated more comments than most, including some great strategy on how to combat the Izzet menace. But since I know that a lot of my readers might have missed the discussion, I thought it was worth repeating some of the advice that was given.
- Don't assume they always have the answers. Izzet is so strong that when they have the perfect hand, you're probably not going to beat them anyway. Sometimes you just have to play as if they don't have the counter to what you're about to do and thus go for the decisive strike, rather than waiting for a better opportunity.
- Defensive creatures aren't a good answer. Between the pump effect of Prowess and Elusive Spellfist being unblockable, holding your creatures back to block is generally not going to be good enough to beat them.
- You won't often be able to win the long game. Thanks to Treasure Cruise, Tormenting Voice, and (to a lesser extent) Anticipate, Izzet can generate a ton of card advantage. Given enough time, they'll be able to assemble a winning combination. Most of the time, you'll want to finish them off before they get to their late game.
- The best answers are bounce, removal, and discard. Get cards out of their hand, take out their creatures, and bounce them back into their hand after they've generated multiple Prowess triggers. Enchantment-based removal like Pacifism or Tightening Coils are great in that they ignore Toughness and don't fill up their graveyard for Delve.