Rule 2.5 works in synergy with rule 2.3 and 2.4
When you craft a spell, you choose the necessary parameters from rule 2.5. The parameters you need are listed in the powers you choose for your spell.
For example: You want to create a spell with the sole power of Learn.

You see, that Learn has two parameters: [Apprentice] and [Domain]
You also see that Learns cost is 5.
Now you choose one item for the parameter [Apprentice], those are listed in Rule 2.5.1 Apprentice.
You either choose “the casting apprentice” “(an apprentices name….)” or “any Apprentice”. Now, the X1, X2 and X3 are telling you the multiplier of this parameter. Say, you chose “any Apprentice”.
Now you choose the second Parameter, [Domain]. You can again choose one of the items listed in the rule 2.5.2 Domain
Say you chose Time. Time’s multiplier is X2.

Now choose a name for your spell and calculate its cost.
The cost of a spell is the sum of the costs of all its powers.
Since this spell consists of only one power, in fact there is only one Power known to us yet, the Spell’s cost equals that of the one Power it has.

It would look like this:
“Chronological dominance”:
Add one level to any Apprentice’s Mastery in Time.

Now the basic cost of Learn is 5. The multipliers of our parameters are X2 and X3 for “Time” and “any Apprentice” respectively.
That means, the total multiplier is 2*3 = 6
The total cost of a power is its basic cost multiplied by its multiplier. In this case:
5 (basic cost) * 6 (multiplier) = 30
Thus, Rule 2.4 and 2.5 serve as lists from which you choose powers and parameters to craft spells according to rule 2.3.
I hope this helps :)

Zefareu updated the GNDT to spend 10 Energy and gain Level 2 Mastery in Time, but I can see no way that this was legal. (No Spells or other rules exist, so far as I can see, that would increase Time Mastery.)

I’ve reverted the game action. Change it back if I’ve missed something.