The original Blackrazor gave the weilder the hit points and levels of the slain victim for 10 minutes per hit die. In AD&D1, kill a hill giant and get about 10 levels and 45 hit points for over an hour and a half.
An old gaming buddy of mine talked about how his character took Blackrazor with him into the "Against the Giants" adventures. Easy to end up with dozens of extra levels and hundreds of hit points throughout each raid. Sick and crazy, before even considering the headache from bookkeeping.
Now slaying a giant with Blackrazor only gives +1d8 temp hit points, +2 strength, and +1 caster level (if a spellcaster is weilding the sword). Go cleave a group of orcs surrounding you and you get +8d8 hit points, +16 strength, and +8 caster level for 10 minutes. Does something say these effects don't stack? Nothing is a named bonus.
Quasqueton