Demonic Sword - Soul Edge

Equip {x}{x}
Equipped creature gets +X/+X and has trample.
If X is larger than 5, it also has first strike.
Equipped creature's name becomes "Nightmare".
{x}, sacrifice a creature: Soul Edge becomes an
indestructible artifact creature with X/X and
trample until the end of the turn. If X is larger
than 5, it also has first strike.