The Explosive
As an Action, the Dwarf may place the explosive at a wall.
It goes up next time it is the Dwarf's turn.
If the Dwarf places it after his movement, it goes up after his next movement.
If he places it before his movement, it goes up before his next movement.
How to do that in detail?
You place the tile below with the white line on a wall.
All the models on red squares receive 2 BP of damage.
The wall disappears.
Furniture on red squares disappears.
All the rest of my rule shall just ensure that you can't use it as weapon like a thrown grenade: Everybody has one turn to get away, monsters as well.

If it is used in corners or on solid rock, you'd have to interpret that a little bit, i admit. Perhaps you can help me finding a good formulation.
However, you may not give it to the dwarf as general equipment as i can imagine some Quests are depending on a careful layout. So give it to him as findable object once in a while, like an artifact.
Here's a recent example where it has been used.
The overall effect was that the group saved 2 BP worth of fighting, likely saving one of them the life. Like a potion of healing, with more fun.
Placement:

Dwarf runs away (they didn't know the size of the explosion)

Booom
































