I just stumbled across a card I've never seen, Piracy.
Until end of turn, you may tap lands you don't control for mana. Spend this mana only to cast spells.
This would have been interesting back in the days of mana burn, but now it seems like this card boils down to "Tap all mana-producing lands your opponents control". I can't see a situation where the opposing player's correct response wouldn't be to simply tap all their lands. If they don't, Piracy's controller can just do it. Or can they?
Spend this mana only to cast spells.
Does this mean they can't just float the mana and not use it? I would think that you could since it says spend which implies that the restriction is only on what you actually spend the mana on.
Is my take on this card correct? (and is there anything interesting you can do with this?)