Karn being a four-mana planeswalker that can draw you cards, protect itself provided you have artifacts, shut off opposing artifacts, and tick up to six loyalty the turn it enters the battlefield are all solid indications that it should find a home in Modern
It struggles against decks that can ignore its threats and against opponents with more card advantage
Tome Scour gives the most looks for a dredger before you cast Reunion
The early submissions demonstrate the different ways of building something for this challenge, from traditional mosaic techniques to including motion
Wald (Forest) with Six Trees You know how sometimes Wizards will print basic lands with art that makes it nonobvious which basic land it's supposed to be (the Kamigawa: Neon Dynasty basics are notorious for this)
Double Colorless Energy is a simple card that provides two Colorless Energy when attached, allowing you to speed up your setup for a Pokemon by a turn