Stalking Stones

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

The List

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

A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn’t matter how long the permanent has been a creature.

Activating the ability that turns it into a creature while it’s already a creature will override any effects that set its power and/or toughness to a specific number. However, any effect that raises or lowers power and/or toughness (such as the effect created by Giant Growth, Glorious Anthem, or a +1/+1 counter) will continue to apply.