Creature and planeswalker spells you cast have affinity for artifacts. (They cost less to cast for each artifact you control.)
+2: Tezzeret deals X damage to each opponent, where X is the number of artifacts you control. You gain X life.
−3: Return target artifact card from your graveyard to your hand.
−8: Exile the top ten cards of your library. Put all artifact cards from among them onto the battlefield.
(03/05/2019)
Affinity doesn't change the spell's mana value. It changes only how much mana you pay to cast the spell.
(03/05/2019)
Affinity can reduce only generic mana in a spell's cost. It can't reduce color requirements.
(03/05/2019)
Tezzeret himself doesn't have affinity for artifacts.
(03/05/2019)
Affinity for artifacts means "This spell costs less for each artifact you control."
(03/05/2019)
If there are any additional costs or cost increases that would apply to a spell with affinity, apply those before applying any cost reductions.
(03/05/2019)
If a spell has multiple instances of affinity, each applies.
(03/05/2019)
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.
(03/05/2019)
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.
