A harpoon is a weapon described on UA 77.

A hit snags the target. When snagged, the wielder of the harpoon can take a G action to drag the target, which does 1 point of damage to the target and moves them 1“ closer to the wielder.

To get un-snagged:

• The target must have INT 2 or higher.
• The target must have some means of dislodging the weapon head or severing the line. If severing the line, the line is automatically hit, and damage is rolled. 2 points of damage sever it.
• A saving through vs poison is allowed (no bonuses to saves vs actual poison are granted; “poison” is merely the saving throw category here). Failure means the snagged creature is dragged as above.

See UA 77 for additional rules and stipulations. Also see the lasso and net.