Embercleave

• WOTC Official Reminder Textofficial rules
  Equip — Equip [cost] ([cost]: Attach to target creature you control. Equip only as a sorcery.)
• WOTC Official Reminder Textofficial rules
  Flash — You may cast this spell any time you could cast an instant.

• WWizards of the Coast2024-11-08
  Official Ruling
  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 increase Embercleave's cost by removing attacking creatures you control.
• WWizards of the Coast2024-11-08
  Official Ruling
  Embercleave's second ability can't reduce its cost below .
• WWizards of the Coast2024-11-08
  Official Ruling
  To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.

Rulings via Scryfall