2019-05-03 : Affinity can reduce only generic mana in a spell’s cost. It can’t reduce color requirements.

2019-05-03 : Affinity doesn’t change the spell’s converted mana cost. It changes only how much mana you pay to cast the spell.

2019-05-03 : Affinity for artifacts means “This spell costs {1} less for each artifact you control.”

2019-05-03 : If a spell has multiple instances of affinity, each applies.

2019-05-03 : If there are any additional costs or cost increases that would apply to a spell with affinity, apply those before applying any cost reductions.

2019-05-03 : In a Two-Headed Giant game, Tezzeret’s first loyalty ability causes the opposing team to lose twice X life and you gain X life.

2019-05-03 : Tezzeret himself doesn’t have affinity for artifacts.

2019-05-03 : The cost reduction is set before you pay any of the spell’s costs. Specifically, you could lock in a discount for an artifact you control and then sacrifice that artifact to activate a mana ability.