[Tools] Weapon - Rubble, Gravel, Sand, Dust

Hammers are not particularly interesting because they're often made for a single purpose (smashing things) but I kinda like the name I picked for this one. Less of an "adjective+noun" or "Proper Noun" kind of name, but simply a collection of nouns that imply a progression.

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The hammer appears like any other mason's hammer, tooled specifically to hew stonework or pound them into place. With the right words, however, it grows to a tremendous size, its properties magnified by tenfold, perfect for master masons who don't much care for a job's secrecy or structures during a quick getaway.

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Rubble, Gravel, Sand, Dust
Weapon (maul), rare (requires attunement by a character proficient with mason's tools)

This weapon is normally the size of a hammer, during which they can used as mason's tools for crushing stone, and allows you to double your proficiency bonus to ability checks made using mason's tools. Creatures unaware of the hammer's properties initially perceive it as a simple tool and can use an action to recognize its true purpose by succeeding on a DC 15 Intelligence (Arcana or Investigation) check.  

True Size. While holding the hammer, you can use a bonus action to speak its command word to enlarge it, provided it has sufficient room to do so. While enlarged, it becomes a maul and grants access to its other properties. You can use another bonus action to speak a command word to return to the size of a hammer. 

Siege Hammer (Maul Only). You have a +1 bonus to attack and damage rolls made with this magic weapon, which deals double damage to objects and structures.

Omni Crusher (Maul Only). This weapon has 3 charges and regains 1d3 charges daily at dawn. As an action, you can expend 1 charge and swing this maul at nonmagical earth or stone no thicker than 3 feet, instantly pulverizing a 5-foot square section of it. Alternatively, you can expend 2 charges to cast shatter from it centered on you (spell save DC 15; you are unaffected by this spell).