One of the first things everyone does to improve their decks is to lower the mana curve of the spells. Very simple and effective. You put in more lower costing spells and remove higher ones. You are also able to play multiple spells a turn and not just play a land then pass. However, where do you put in spells with an "X"cost in it? What about keeping up mana for counter spells or activated abilities? These are spells that will "Shift" their casting cost depending on your turn. Confused? So was I at first but let's go through this train of thought. Shifting Casting Costs What I mean by a spell's ability to shift its casting cost is just that. The spell becomes more effective after a certain amount of turns so it will go up or down the mana curve. Counter spells are probably the best example here. Let's look at [Negate] which counters a target non-creature spell with a casting cost of 1 colorless and 1 blue so it has a converted mana cost (CMC) of 2. Most would put this card in the 2 CMC slot of their curve, while I will put this in the 4 CMC spot. The reasoning for this came about as I found myself always dreading to find a counterspell in my opening hand with no other 2 cost spell. For some this opening hand is great as you can leave the mana up during your turn to counter something. However, the likelihood of you actually countering a spell this early in the game is very small. Normally, one card isn't bad but let's say you have four counter spells in your deck with the same mana cost of 2. That's a lot of possible dead cards early game for you where turns are very important. Moving up the CMC of the spell and placing more 2 CMC spells will make your deck flow better. On turn 4 though the spell would "shift" and go down to a 3 CMC slot with a minimum of 4 mana that can be produced. You should have a number of spells that may be cast while leaving up mana for the counter if needed at this time. X Casting Cost So with counter spells the more mana you have the closer to the actual CMC you get. What about "X"spells though? The official ruling is that the CMC will always be zero and you decide what the value is when casting it from your hand. So a [Fireball] with a casting cost X colorless and a red has a CMC of one. Technically, this goes into the 1 CMC slot as X is zero. Maybe your deck does cast this for zero damage but the majority don't. For this I look at the minimum that I am willing to put into for the casting cost which is normally 4. Why 4 mana you're asking? There's a reason why not many people run [Lightning Bolt] in commander decks. Plus, there are 486 commanders with toughness less than 4 and for the one extra mana you include another 198 commanders. That's 684 commanders at time of this post which is around 70% of the commanders out there. As more mana is available the CMC can go up as the range of mana I can put into the spell goes up. [Endless One] is a Eldrazi creature with X casting cost and enters with X +1/+1 counters. You can cast this for zero and it will die right away but as you gain access to more mana the possibility that you will, grows smaller. For me, I would place this in the 1 CMC slot as that is the minimum I am willing to pay. As I get more mana the range goes up and it will climb up in the mana curve. Activated Abilities Chances are you have spells that use activated abilities in your decks. They may tap for mana, draw you a card, give counters to something, etc. Some of these you can use right away but what about those that require mana to activate? [Temur Sabertooth] is a 2 colorless 2 green creature for a 4/3 with the following ability. (1)G: You may return another creature you control to its owners' hand. If you do, Temur Sabertooth gains indestructible until end of turn. Cast it out on turn 4 and you are good to go right? What if you have an important creature on the board? Do you want to risk loosing both creatures or wait for that 2 extra mana so that you can save them? When you have spells with a cost to the activated ability then it should be considered into the curve if you want to use the ability right away. When you don't you are leaving a nice juice target that you hope stays on the board for when your turn comes around again. So it stays in your hand and you wait which means you have a dead card until you get enough mana to throw it down on the board. Is Your Curve Correct So how does your decks' mana curve look if you incorporate these new changes to the CMC? When I first made these changes it showed me why my decks were slower than I expected. Making these small adjustments caused them to become more consistant when playing and allowed me to enjoy them more. It also made me a better player as I didn't have to worry about making hard decisions such as when to leave mana up or not. After all, when you don't make hard decisions and know what is efficient for casting spells you get less frustrated with the deck and spend time enjoying the game.