A huge indestructible anvil could be a very good weapon for this game.
The player can use it like the air/mine/flame strike, and the anvil will teleport/be dropped by a helicopter on the target. It will not do a lot of damage to the ground itself, maybe just flatten it a little, but it should do massive amounts of damage to any hogs that are underneath, and bury them underneath, if they happen to survive.
It should also be indestructible so that weapons do not affect it. It can act as a barrier that way. It should however slide or tumble down a slope, if enough ground from underneath it is destroyed, again doing damage to any hedgehogs.