Creature and planeswalker spells you cast have affinity for artifacts. (They cost less to cast for each artifact you control.)
+2: Tezzeret, Master of the Bridge 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.
Affinity can reduce only generic mana in a spell's cost. It can't reduce color requirements.
03-05-2019
wotc
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
wotc
Affinity for artifacts means "This spell costs {1} less for each artifact you control."
03-05-2019
wotc
Tezzeret himself doesn't have affinity for artifacts.
03-05-2019
wotc
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.
03-05-2019
wotc
Affinity doesn't change the spell's mana value. It changes only how much mana you pay to cast the spell.
03-05-2019
wotc
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
wotc
If a spell has multiple instances of affinity, each applies.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.