Mana
From CMC Wiki
Mana is the mystic energy used in calling monsters, casting spells, powering abilities, creating effects, moving to locations, and anything missed that has a listed mana cost. In CMC mana costs are denoted by some combination of the three color symbols with a number after each one. The three color symbols are 
for Dark mana, 
for Light mana, and 
for Gray mana.
Mana naturally generates at a rate of 111 per turn. Other ways of getting mana include playing Generators, mana Sources, mana-giving spells (like Sunflare), mana-giving abilities (such as that of the Time Waster). Mana carries between turns.
Some cards just set mana to a specific value. Examples include Mana Explosion (all values set to 10 for both players) and Feedback (all values set to 0 for target player).
Certain cards have abilities which use a player's mana as a variable in their effect:
- Feedback (Deals 3x target player's mana in direct damage)
- Firestorm (Deals 3x caster's
count in direct damage and its caster loses all Grey Mana)
- Prismatic Golem (Gains temporary attack based on one of its controller's mana colors depending on the the receiver of damage)
- Eikre (War) (Has a Constant attack bonus equal to his controller's
count)
- Year Two Cake (Gives Caked, which includes temporary life changes based on a comparison of total manas)
- Dragon (VCH) (Gains attack and life on draw phase equal to controller's
and counts, respectively)
- Tesla (VCH) (Snipe damage is equal to her controller's 5+ count)
- Ninja no Niji (Gains temporary attack and life on draw phase equal to controller's and counts, respectively)
The Feedback card when self-targeted used to give negative mana, which revealed some about the way mana and spells are treated. This has since been fixed. Point one in the list below is likely now false.
1. When using something first the check to see if the player has enough mana is run, then whatever the mana is being used for happens, then the mana cost is deducted. If the cost were deducted first than the player would end up with mana of every color. Instead, they end up with 00 -15.
2. Cards have a hidden "cost" of 0 mana of whatever types a card doesn't have a listed cost for. This is shown by the fact that it is impossible to play any cards while having negative mana.
