I'm saving the more flexible "Add one power of any type to your power pool" till the second set, like the [1] symbol that can be paid with one power of any type.

This is a rather nice card in the set. Does a decent job of feeling like each mapping is in flavour, too (although Discard is a tad breaking-the-fourth-wall!)

Heh. It is somewhat. I'd love another cost, but I don't think "Sacrifice a planeswalker" is very sensible... :) I was thinking of the Odyssey atogs, which had "sac an artifact", "sac an enchantment", "sac a land", "discard a card" and "exile 2 cards from graveyard" as their costs - no "sac a creature". But the flavour of throwing creatures into your engine to get chemical power is rather irresistible.

Hm. I know what Chris means, although "discard" does have an appropriate waterfall feel for torque. Even more flavourful would be "tap an untapped permanent you control and untap a tapped permanent you control" or perhaps "put a card from zone A into zone B and a card from zone B into zone C" but I can't imagine how that would work mechanically.

You could self-mill, but that's very little cost and still has a 4th-wall problem. I think probably Discard is the best you'll get.