The List

Stalking Stones

{T}: Add {C}.
{6}: Stalking Stones becomes a 3/3 Elemental artifact creature that's still a land. (This effect lasts indefinitely.)

Tempest Remastered

{T}: Add {1} to your mana pool.
{6}: Stalking Stones becomes a 3/3 Elemental artifact creature that's still a land.

Duel Decks: Elspeth vs. Tezzeret

Mirrodin

{T}: Add {1} to your mana pool.
{6}: Stalking Stones becomes a 3/3 artifact creature that's still a land. (This effect doesn't end at end of turn.)

World Championship Decks 1998

Tempest

oc
T: Add one colorless mana to your mana pool.
o6: Stalking Stones becomes a 3/3 artifact creature permanently. (This creature still counts as a land.)