Alright: if I'm going to offer constructive criticism on others' ideas, I should put mine up for scrutiny as well.
The idea of this card is an energy hoser, but unlike
solemnity - which prevents energy production - this would be a card that allows for a tax on using energy. A few ideas:
Sorcery - Diffusion Field, 3W- until your next upkeep, all energy costs are doubled.
I'm not married to the 4cmc, I just thought that would be fair, letting an opponent get off one or two energy effects before tax could be played.
Another 'dial' to tweak the card would be to make it an enchantment with an activation cost; that way you could split the cost, say 2W to cast, 1W to activate. If it can be activated multiple times, I like the idea of requiring the enchantment activation to use expendible counters that would be an etb trigger, sac it when no more counters are left. Bonus is that would prevent it from comboing so much with
solemnity avoiding an overly oppresive energy lock.
If this would be in black, you could make it be a energy tax that saps the life of the energy user. Say....2BB enchantment, at each end step, each player that used energy this turn loses 5 life; if no opponents used energy this turn, you lose 2 life or you may sacrifice this enchantment. Ok, maybe that one needs more work.
(Can you tell I'm hoping energy will return as a mechanic? But next time better answers are needed, I think we can all agree)