Here's an example to get this started: Volcano slopes.
I envision charred earth, maybe a few patches of dried grass here and there. One or two blocks of rock ejected from the crater may also be present on tiles (blocking line of sight, indestructible, not rooted).
In addition there should be a few tiles of glowing lava. Passing through these would cause 1 damage to non-flying characters. Standing on these would equally cause 1 damage at the beginning of one's turn.
Lastly some of the tiles would show cracks. Only visual appearance thus far, at least until the volcano wakes up...
The volcano waking up would indeed be the key feature of this environment.
At random frequency (probably set so that it typically happens once or twice during a battle), the volcano would emerge from its apparent sleep, causing the following to happen:
- the whole playfield sees tremors (screen display "shaking" + device vibration on if equipped + rumble sound)
- all units tend to lose balance, moving them 1 space in a random direction (if the space in that direction is empty). This may cause them to end up on a lava tile (ouch!), or on a tile with cracks...
- toxic fumes are then expelled from the tiles with cracks, inflicting poison (1) to any unit standing there.
- and lastly as hell unleashes, an additional rock falls from the skies on a random tile, destroying decor on that tile if any, and dealing 4 damage and knocking back (2) in a random direction any unit standing on that tile.