Blackblade Reforged
Legendary Artifact — Equipment
Equipped creature gets +1/+1 for each land you control.
Equip legendary creature legendary creature 
Equip 
It spilled the blood of one elder dragon. In Gideon's hands, it may yet taste another's.
Chris Rahn
Rulings
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.
(wotc • 2018-04-27)
"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."
(wotc • 2018-04-27)
Printings
Rulings
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.
(wotc • 2018-04-27)
"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."
(wotc • 2018-04-27)