There seems to be a magic mana number in the game and I'm starting to think that number is 2. Anything that is one or zero mana is clearly a) underpowered (Healing Salve) or b) crazy (Force of Will) or c) crazy in the right deck but otherwise meh (Invigorate in infect decks). Very, very few cards hit the 1 mana 'playable and solid' line-Duress comes to mind with Lightning Bolt being at the high end of the power spectrum.
At two mana though, this is where the rubber starts to meet the road. Nearly every deck gets to two mana in nearly every game so what you can do with it matters and Magic is packed with cards that are truly useful at that converted mana cost. You can even see it in Standard, where at the last Born of the Gods event, the highest concentration of cards was at the 2 CMC slot. One of the most powerful spells, Counterspell, is at two mana and it choked so much design space out of the game WotC had to push hard counters back to three mana-although it took them years to do so.
I think it's also why so many limited environments are designed with cards to hit 2.x on the curve. A deck that can reliably do something on turn two, every time, means fast, demanding games that are more luck oriented but if you push the curve to three, deckbuilding skill and card evaluation start to come into play and as you see more of your deck, variance is decreased.
In constructed this is a different animal, of course because you can develop decks that can turn things around on turns 3 or 4 to give you a chance to win. Nevertheless, after my experience against the Painter's Servant deck where I would have had an opening to win, if I had kept Pyroclasm in, I've been thinking about it more.
This motif repeats: The Prismatic Prism in My Curse, Black Sun's Zenith in Slave to the Grind and Wall of Omens in Perpetual Motion.
All these decks had problems with
solutions coming at the 2 CMC slot. I discovered these solutions after I
was finished talking about them on the blog; that frequently happens.
Decks I write about stay in playing rotation for a little while to
work out any kinks, longer if I have an identifiable problem or question
that I can work on. If it's just a 'blarh, this isn't working and I
don't get it' then I let it rest. Eventually, a solution comes to mind or a new card is printed to solve problems.
None of these solutions are what I'd call gamebreakers; they don't have the power of something like Snapcaster Mage or Tarmogoyf but they end up being the glue that helps hold the decks together. This is a good thing to keep in mind when looking at where to go with a deck that has hit a stumbling block.