From Worms Knowledge Base
This weapon, dropped like a dynamite when used, hits the ground with a loud, metallic thud and no bounce. And doesn't explode. Useless? Far from it.
When dropped on a worm, the Anvil causes significant damage. The damage it inflicts is directly proportional to the speed with which it hits the worm. That is to say, damage is determined by how far the anvil falls, like fall-damage only on a much bigger scale. Furthermore, the anvil remains where it is after use, acting like an indestructible unexplodable barrel. When the land beneath it is shot, it falls down again, inflicting yet more damage on any worms in its shadow.
Programming isn't likely to pose any problems with this one, seeing as it is dropped like a dynamite and acts like a barrel throughout the rest of the game. One point to bring up however is what exactly happens to the worm that gets squashed by it, since the anvil remains as an object afterwards.
Logically, the worm should get its head stuck in the ground after being struck, in the same way as it would for a Battle Axe attack. Then, when it recovers, it should pop up to a height great enough for it to land on top of the anvil.
It would be easy to create maximum damage if you happen to have a rope, as you could drop the anvil from the greatest height achievable, with relative ease. Also makes for an annoying blocking weapon, as it acts as an invulnerable solid object that can only be moved if the land beneath it is destroyed, which would be impossible with indestructible terrain.
Another weapon in-keeping with the cartoon style - no cartoon goes without the Anvil. It is also unique in its mechanism and would make a good addition to Worms gameplay.