Mycosynth Golem

• WOTC Official Reminder Textofficial rules
  Affinity — This spell costs less to cast for each [quality] you control.

• WWizards of the Coast2004-12-01
  Official Ruling
  The spells gain affinity for artifacts as they’re put onto the stack. They don’t have the ability while they’re cards in your hand.
• WWizards of the Coast2004-12-01
  Official Ruling
  Two or more instances of the affinity ability are cumulative, even if they’re both affinity for the same thing.
• WWizards of the Coast2004-12-01
  Official Ruling
  If Mycosynth Golem is sacrificed as part of the cost to cast a spell, the cost reduction will already be locked in, and the cost won’t be increased.

Rulings via Scryfall