Anvil
From the Super Mario Wiki
The dreaded anvil was a weapon of old used once by the Koopa Troop. A horrid device, it was used as an execution device atop Yoshi's Island by the Black Shy Guys. Anything crushed was either highly injured, or killed immediately.
The Anvil first appears in Super Mario Land 2: 6 Golden Coins. Near the end of Wario's Castle, the anvils fall and raise from the ceiling.
Anvils another appearance in the final pages in Yoshi's Story, where they were carried menacingly by the Black Shy Guys inside Bowser's Castle. If a Yoshi should wander near the anvil-carrying Shy Guys, the Black Shy Guy would drop the giant, spiked anvil and crush whatever was beneath it. They appeared in the Lift Castle and Ghost Castle, although they did appear in the Mecha Castle.
Anvils reappeared in Mario & Luigi: Superstar Saga, but was not as a weapon, and they only appeared in Hoohoo Village and the Beanbean Kingdom.
