Can I exhaust Daughter of the Void to add floating power, then conquer Hall of Legends and pay 1 energy to ready Daughter of the Void, then play Falling Star by tapping Daughter of the Void again and use both powers from Daughter of the Void?

Ruling: Yes, this sequence is completely legal. You can float power from Daughter of the Void before conquering Hall of Legends, use the Hall trigger to ready her by paying 1 energy, then exhaust her again to generate a second power, and finally use both floating powers to help pay for Falling Star.

Sequence:

• Exhaust Daughter of the Void to add 1 power to your Rune Pool (this power has the restriction "Use only to play spells")
• Win combat and conquer Hall of Legends, triggering its ability
• When the trigger resolves, pay 1 energy to ready Daughter of the Void
• Exhaust Daughter of the Void again to add a second power to your Rune Pool
• Declare you are playing Falling Star and pay its cost using the 2 floating powers from Daughter of the Void plus 2 energy from runes

Nuances:

• Power generated by Daughter of the Void has a restriction that it can only be used to play spells, but it remains floating in your Rune Pool
• The Rune Pool only empties at the end of your draw phase and the end of your turn, allowing you to float resources across actions
• The Hall of Legends ready cost is paid with energy, not power, so Daughter of the Void's restriction doesn't prevent this interaction
• Because Falling Star is a spell, using the restricted power from Daughter of the Void satisfies her ability's requirement