Karn, Living Legacy

For Karn’s second loyalty ability, you don’t choose how much mana to pay until the ability resolves. Once the ability begins to resolve and you have paid, no player may respond until you have finished all the steps of that ability.

Karn’s emblem has an activated ability that allows you to tap untapped artifacts to pay its cost. Notably, you may tap artifact creatures that entered the battlefield this turn to pay this cost, even if they don’t have haste.

Powerstone tokens are a new kind of predefined token. Each one has the artifact subtype “Powerstone” and the ability “{T}: Add {C}. This mana can’t be spent to cast a nonartifact spell.”