I control Conspiracy naming Samurai, as well as Kentaro, the Smiling Cat. I then attempt to play a creature spell with {X} in its mana cost, such as Maga, Traitor to Mortals. Suppose I have 13 mana available, but only two of it is black, so I elect to use the alternative cost from Kentaro (which, relevantly for rule 107.3b, is an alternative cost that still contains X, but this X is defined differently). How many of these options end up being legally available?

-Pay 0 mana, get 0 counters
-Pay 3 mana, get 0 counters
-Pay 3 mana, get 3 counters
-Pay 13 mana, get 10 counters
-Pay 13 mana, get 13 counters

Edited Russell Jones (Dec. 1, 2015 11:01:35 PM)

Sorry for the delay on some of these questions. Some of these questions involved a lot more discussion, and some just slipped through the cracks. We're going to play a little catch-up now.

The X in Maga's cost only looks at the X in its mana cost, not if X is used for any other reason while casting it. You're free to cast Maga with X=3, and using Kentaro, choose to pay 6 instead of the normal mana cost. Maga will use the value you picked when you announced it, not the X that Kentaro was using, because the Xs are being used in different contexts. If you cast Maga with X=3, and use Kentaro's ability to cast it by paying 6, Maga will enter the battlefield with three +1/+1 counters on it.

Nathan Long
Magic Rules NetRep