Can Vex and Irelia Graceful attacking the same battlefield allow playing Discipline targeting Irelia for free (reducing cost from 1 to 0)?

Ruling: Yes, you can play Discipline for free. When paying costs, you can apply cost reductions in any order, so you can apply Vex's reduction first (getting the spell to 1 energy minimum) and then apply Irelia's reduction to get it to 0 energy.

Sequence:

• Apply Vex's cost reduction first (reduces to minimum of 1 energy)
• Apply Irelia's cost reduction second (reduces to 0 energy)
• Total cost is 0 energy

Nuances:

• The order of applying cost reductions is flexible during cost payment, not determined by layers or timestamps
• This is handled by the cost payment rules rather than the layer system