Power Artifact

Enchant artifact
Enchanted artifact's activated abilities cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Magic Online Promos

Masters Edition IV

Enchant artifact
Enchanted artifact's activated abilities cost {2} less to activate. This effect can't reduce the amount of mana an ability costs to activate to less than one mana.

Antiquities

The activation cost of target artifact is reduced by o2. If this would reduce target artifact's activation cost below o1, target artifact's activation cost becomes o1. Power Artifact has no effect on artifacts that have no activation cost or whose activation cost is o0.

Can be placed on artifacts with no or zero activation costs, but this has no effect on them. It does not increase the cost to one.

Only affects the generic mana part of activation costs. Colored parts of mana costs are not affected.

Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities and will have colons in their reminder text.