A good rule of thumb is to read each card as though it was talking to you directly, with you being both the player and the mage. So when it says to gain two mana, I would presume it means for you to gain two mana. Since it is talking to you. If it said the caster gains two mana, that'd be different.
TLDR: I agree with Mystery. The mage gains it.
P.S. it's not really specified anywhere though. That's just me applying logic that has worked well in the past.