Xanathar's Guide to Everything includes the spell shadow blade, which seems
intended to be used only by the caster. It creates an actual weapon (XGtE, p. 164):
You weave together threads of shadow to create a sword of solidified gloom in your hand.
However, the spell also says:
If you drop the weapon or throw it, it dissipates at the end of the turn.
Instead of dropping or throwing the sword, what happens if the caster hands it to an ally? Can that ally attack with the sword on subsequent turns (in particular, without either party using Ready to act on the same turn)? Would the sword dissipate if an ally was the one who dropped or threw it?
Best Answer
It Would Dissipate
The Rules as Intended, and official ruling in Sage Advice is that it would dissipate.
If it Didn't
If you ignore Sage Advice and read "drop" differently than Rules Designer Jeremy Crawford, all you have is what is in the shadow blade spell:
Note, this literal reading has drawbacks and a few problems. The drawback is that you wouldn't be able to summon it back unless you drop or throw it, and the other character couldn't gain the proficiency benefit from the spell, nor the advantage from dim light or darkness.
The issues with this literal reading are that a player you passed it would be able to drop or throw it, and it wouldn't be able to be called back to you. These issues are likely an artifact of the intent of the designers not matching the words they wrote. So, ask your DM before you try it, or try it in game before a fight so you're not caught off guard.