Potion of Blunt Damage is created by combining the reagents shown below. Note: If the third reagent slot is shown empty, this means that any reagent can be placed in that slot (You still need to have all three reagent slots filled to be able to create a potion).
Lime Green Mushroom
Neon Gem (Added in 2.4)
The duration of the Potion of Blunt Damage is as follows: