There's a bit of an issue if you can plant 4-5 of those templates on a board...i mean for a normal bash, it's not a problem as you can go around it, it's when it comes to scenarios that the spell gets very gimmicky.
Cross the bridge: just cast that thing on the bridge and it's game over (imagine two).
Take and hold: a bit like the bridge, it can prevent access to the objective.
Sieges: cast in front of the gate.
Doing residual damage 12, only the most powerful pieces in the game can dare to go through a single time, let alone the other side.
While fluffy and worthy of a "fire bender" movie style, it can transform a game to a non-issue quickly.