Ultra Hammer

The Ultra Hammer is one of the most powerful weapons in Mario's possession.

Super Mario RPG: Legend of the Seven Stars
The item first appeared in Super Mario RPG: Legend of the Seven Stars. In this game, the Ultra Hammer is Mario's second most powerful weapon.

Paper Mario and Paper Mario: The Thousand-Year Door
In Paper Mario and Paper Mario: The Thousand-Year Door, the Ultra Hammer is Mario's strongest hammer. In battle, a timed Ultra Hammer attack deals six points of damage to a defenseless enemy without attack-raising badges (while Mario's normal Hammer only delivers two).

In Paper Mario, the Ultra Hammer is found in the caverns of Mt. Lavalava, and allows Mario to smash Metal Blocks with it. It can also be used to flip hidden panels on the ground, revealing Star Pieces from underneath.

In Paper Mario: The Thousand-Year Door, the Ultra Hammer is found inside a chest placed on a high platform in Rogueport's plaza that Mario must use the Spring Jump to dislodge it from underneath. This Ultra Hammer has been downgraded somewhat from the previous game in that it can destroy Stone Blocks at the most and cannot reveal Star Pieces in the ground.

Mario & Luigi: Superstar Saga
In Mario & Luigi: Superstar Saga, the Ultra Hammer is the third and last Hammer upgrade Mario and Luigi receive. With it, they can break black rocks on the field. The Hammers are not any stronger in battle, though. This Ultra Hammer lacks the red stripe.

Trivia

 * In Super Smash Bros. Brawl, Golden Hammers resemble the Paper Mario series's version of the Ultra Hammer.
 * Just like the Yoshi Kid's Gulp in Paper Mario: The Thousand-Year Door, Ultra Hammer (along with Super Hammer) only does its base damage to enemies attacked behind by the front enemy regardless of upgraded attack power.