You have at least two opponents who each control at least one artifact.
Mana Needed
({1} magic symbol) plus enough mana to pay for commander tax, if applicable available.
Steps
Cast Journey On either from your hand or from the command zone by paying ({1} magic symbol) and commander tax, if applicable, creating at least three Map artifact tokens and exiling Journey On with the ability to cast it from exile.
Activate
Krark-Clan Ironworks by sacrificing three Maps, adding six ({C} magic symbol) .
Cast
Kellan from exile by paying ({2} magic symbol) .
Activate
Meticulous Excavation by paying ({3} magic symbol) , returning
Kellan from the battlefield to your hand.
Repeat.
If you have at least three opponents who each control an artifact, once you have infinite mana, you may forego sacrificing the Maps, and you may use the Maps to put infinite +1/+1 counters on creatures you control.