Crafteable or Purchasable or Permanently deployed at public locations.
Either deployable or via dialog in Tent/Base. Other solution is public locations only, this forces some social aspect as players aren't hidden in private instances.
Parameters of the dummy can be set via dialog, or preset dummies available with most common protections.
Dummy has 400 HP
If Dummy is not damage for 5 seconds, it will regen to full HP.
If Dummy is below 0 HP, it will pop up to max immediately, displaying some killing info, dps, whatever could be useful etc.