Karn, Scion of Urza
Oracle Text
+1: Reveal the top two cards of your library. An opponent chooses one of them. Put that card into your hand and exile the other with a silver counter on it.
−1: Put a card you own with a silver counter on it from exile into your hand.
−2: Create a 0/0 colorless Construct artifact creature token with "This creature gets +1/+1 for each artifact you control."
Card Rulings
4/27/2018 A token created by Karn’s last ability will count itself, so it’ll be at least 1/1.
4/27/2018 Karn is colorless but not an artifact. The Construct tokens created by Karn’s last ability don’t count Karn.
Cost seems a bit too high for Affinity. The ability to produce 3 constructs over 4 turns made me consider shoving it in the sideboard to replace master of etherium against decks with a glut of removal... but that's what Etched Champion is there for.
Definitely see a possible use in older formats where 0- and 1-costed mana rocks are plentiful... but creating a bunch of vanilla dudes seems a bit slow for such formats (especially compared with the explosive speed of creatures like Hollow One or Vengevine).
the artifact token ability is just useless as it reads so far. this is a leak maybe the writing will change later. If anything this ability is just for making up for the fact that karn liberated had no artifact theme to any of its abilities. depsite karn squarely relates to artifacts in the storyline.