Can you play Call To Glory with 0 energy if you choose to spend a buff instead of paying the 3 resource cost?

Ruling: Yes, you can play Call To Glory without having 3 energy available if you choose to spend a buff instead.

Sequence:

• Calculate the cost first before paying
• If you opt to consume a buff, the cost becomes only spending a buff with no energy required
• Pay the calculated cost

Nuances:

• Energy and Power work with a Mana Pool system, so you don't need to pay immediately when playing the spell
• The buff spending is an additional cost option that replaces the energy requirement