The Magic Mirror

If a split card is both an instant card and a sorcery card, it's only counted once for The Magic Mirror's cost reduction ability.

Once you announce that you're casting a spell, no player may take actions until the spell has been paid for. Notably, opponents can't try to change by how much a relic's cost is reduced.

The cost reduction ability reduces only the generic mana in the relic's cost. The colored mana must still be paid.