Does Vex's ability make opponents pay 1 energy + 1 power when they play a hidden card during combat?

Ruling: Yes, Vex's ability applies to hidden cards. Hidden sets the cost to 0 first, then Vex's cost increase is applied afterward, resulting in a total cost of 1 energy + 1 power.

Sequence:

• Hidden sets the card's cost to 0 (ignoring base cost)
• Cost increases are then applied
• Vex's passive adds 1 energy + 1 power as a cost increase
• Final cost is 1 energy + 1 power

Nuances:

• This only applies if combat has actually begun at the battlefield where Vex is present
• If Vex just moved but combat hasn't started yet (e.g., with "When I move" triggers still resolving), the additional cost would not be active
• Vex's effect is a cost increase, not an additional cost, which is why it applies after hidden's cost reduction