Instant, 1G (2)
Common
Until end of turn, target creature gains trample and gets +X/+X, where X is the number of attacking creatures.
"The hermit dies. The outcast dies. The lone wolf dies. Only those who stick together survive this world."
—Uros, Pendelhaven elder
Illus. Ron Spencer

9/25/2006: The bonus is determined when the spell resolves.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern