Writhing Necromass

• WOTC Official Reminder Textofficial rules
  Deathtouch — Any amount of damage this deals to a creature is enough to destroy it.

• WWizards of the Coast2022-09-09
  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 (such as that of Writhing Necromass). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.
• WWizards of the Coast2022-09-09
  Official Ruling
  Writhing Necromass’s first ability can’t reduce the in its cost.

Rulings via Scryfall