Say you have a card that says 'reduce by X the next Y card you play'. But you have another ability in play that says 'increase the cost of the next Y card you play by X'. Which modifier gets applied first? (An example of this is K2SO and Rearm)

Does it matter? The end result of X+2-1 or X-1+2 is always X+1.

36 minutes ago, Amanal said:

Does it matter? The end result of X+2-1 or X-1+2 is always X + 1.

Fixed that for you.

Sorry my brain is not firing all cylinders today. But what if one card says double and another says reduce by 1. (I am new to Destiny so I don't know of a card that doubles cost of another card.) Do we follow math rules and double then subtract or can we reduce then double?

3 hours ago, dhowtocor said:

Sorry my brain is not firing all cylinders today. But what if one card says double and another says reduce by 1. (I am new to Destiny so I don't know of a card that doubles cost of another card.) Do we follow math rules and double then subtract or can we reduce then double?

In the absence of any other instruction that would make the most sense.

It also obviously depends on the other words surrounding the modifier such as "before" "after" or "when".

You choose the order if all your effects have the same timing window.