Why can't Blue Sentinel's power be used to pay for Power Nexus's optional cost?
Blue Sentinel gives you power at the start of your next main phase when you hold a battlefield with it, while Power Nexus lets you optionally pay power as part of an ability that resolves during the beginning phase's hold triggers. A player wondered why they couldn't use the power from Blue Sentinel to pay Power Nexus's cost, since a "you may pay X to do Y" cost is normally paid on finalization rather than immediately when the ability is put on the chain. Why can't Blue Sentinel's power be used for Power Nexus's cost?


