Karn's power and toughness are each equal to the greatest mana value among artifacts you control. At the beginning of your upkeep, add {C} for each artifact you control. This mana can't be spent to cast nonartifact spells. Until end of turn, you don't lose this mana as steps and phases end.

You may look at the top card of your library any time. You may cast artifact spells and colorless spells from the top of your library. {T}, Pay 1 life: Exile the top card of your library.

{T}: Add {C}. If you control an Urza's Mine and an Urza's Power-Plant, add {C}{C}{C} instead.

{T}: Add {C}{C}{C}.