Can Lux Crownguard's ability (gain 2 energy, use to play spells only) be used for 2 different spells, and can it be used for one spell first and then another spell later?

Ruling: Yes, you can use Lux's 2 energy for multiple different spells. You can "float" energy in your rune pool, meaning you generate the energy and use it later in the turn, even splitting it across multiple spells.

Sequence:

• Use Lux ability to generate 2 energy
• The energy enters your rune pool as floating energy
• Spend the energy on spells at any point during your turn (can be split across multiple spells)
• Any unused floating energy disappears when your rune pool empties (at draw step and end of turn)

Nuances:

• You don't channel new runes when using Lux, you just create energy
• Floating energy/power disappears if not used before the rune pool empties
• Your rune pool empties at the draw step and at the end of each turn
• Runes themselves stay tapped/untapped; only floating resources disappear