"Don't worry, be emo"
1E030100 Add Damage
parameter 1-Scalar: Damage to Add.
Happy Holidays! (or Emo Holidays.)
...and to make it so that it works when you hit them, you can do this:
Set Loop for however many frames you want the hitbox(es) to last:
If: 0B (0B is if hitbox connects)
Synchronous Timer: 1 frame