Cool thing about terraforming spells in FE:LH is that they can place Stamps (pre-generated terrain pieces). You should check out the volcano spell if you want to push the envelope with terraforming.

Update coming soon with more graphics and balance fixes.

In Children of Storm there is an item called the Horn of Resounding which uses a 13x13 stamp. 

Isn't there a spell condition you can set that the target tiles have to be empty? What happens if you set <SpellTargetType>EmptyTile</SpellTargetType> and maybe <SpellTargetTileOccupied>Empty</SpellTargetTileOccupied>

Exactly what I saw when I toyed around - I am guessing the reason Curgen's Volcano is so expensive, and there is no create mountain spell or other terraforming spells, is because they know how abusable they could be.

Also, I noticed that placing in a stamp in water doesn't work as intended, the engine will place land in water but will default it to beach or plains.

I might PM you guys(heavenfall/primal) on this, I've spent a lot of time tinkering around with terraforming in this engine but you likely still know more than I!

Major update incoming!

updated to 1.0!