People are asking if controlling Kruphix changes what happens when you get hit with a Drain Power. If it's valid to say that mana in your mana pool only becomes ‘unused’ at the end of step or phase, then Kruphix shouldn't affect it.

Comprules is still giving an “empty” to Drain power in
106.11. One card (Drain Power) puts all mana from one player's mana pool into another player's mana pool. (Note that these may be the same player.) This empties the former player's mana pool and causes the mana emptied this way to be put into the latter player's mana pool. Which permanents, spells, and/or abilities produced that mana are unchanged, as are any restrictions or additional effects associated with any of that mana.

…and Kruphix, God of Horizons has an “instead” replacement for “empty”

Google didn't turn up nearly enough threads concerning this, so I thought I'd start one here. The only other one I found was http://www.mtgsalvation.com/forums/magic-fundamentals/magic-rulings/magic-rulings-archives/558159-kruphix-and-mana-short-drain-power-power-sink

Nope. The mana that's being removed from the Kruphix player's mana pool via Drain Power is not unused mana, so Kruphix's ability will not apply to it. “Unused mana” is effectively mana left over in the mana pool as a step or phase ends, not mana that just happens to be in the mana pool when Drain Power resolves. The mana will be drained from the Kruphix's player mana pool like normal and the player who cast Drain Power will get that mana.

Nathan Long
Wizards.Com Boards NetRep