Imperial Taxation (formerly Vow of Poverty)

[Ephraim]

Then your mana pool doesn't empty until the spell resolves, which means you can float mana to pay for things while the spell is still on the stack (one of the possibilities I want to prevent.)

[Matt]

Players can only play mana abilities while playing or resolving another spell or ability.
As any spell or ability is put on the stack, empty that spell or ability's controller's mana pool.

Would that work? I know it's ugly but I want to know if it's even possible to word this correctly first, then we can work on the aesthetics. I added the "or resolving" thing to allow for Nether Void and Mana Leak.

[Godder]

Without getting into another game's mechanics too much, floating mana (gold) doesn't exist in L5R without using storage cards. If the desired effect is simply to replicate the inability in L5R to spread mana (gold) from one source (holding) between multiple spells/abilities (effects/cards), then the proposed wording is fine.