"Tempered in the blood of ten thousand sacrifices? Superstitious drivel."
—Mishra, note to his researchers

Blackblade Reforged

Equipped creature gets +1/+1 for each land you control.
Equip legendary creature {3}
Equip {7}

The Brothers' War Retro Artifacts

It spilled the blood of one elder dragon. In Gideon's hands, it may yet taste another's.

Dominaria United Commander

Neon Dynasty Commander

"Equip [quality] creature" is a variant of the equip keyword. "Equip [quality] creature [cost]" means "[Cost]: Attach this Equipment to target [quality] creature you control. Activate only as a sorcery."

Whether the target creature is legendary is checked only as Blackblade Reforged's first equip ability is activated and as that ability resolves. If the creature somehow becomes nonlegendary later, Blackblade Reforged remains attached to it.