Lucky charm

Lucky charms are the life gaining artifacts in the Alpha (set) Crystal Rod, Iron Star, Ivory Cup, Throne of Bone and Wooden Sphere. They were printed in every Core Set through 8th Edition. Their improved versions came out in Darksteel; Angel's Feather, Demon's Horn, Dragon's Claw, Kraken's Eye and Wurm's Tooth and they have been printed in every core set afterwards.

The original lucky charms for white read:
Whenever a player plays a white spell, you may pay . If you do, you gain 1 life.

The version from Darksteel read:
Whenever a player plays a white spell, you may gain 1 life.

The newer versions require no activation cost. They just cost more to cast.