Since you last played
UntouchedValve’s patch notes record no changes to Mithril Hammer since patch 7.06d (mid 2017). It works the way you remember.
What it does now
- + 24 Damage
Shop item, 1,600 gold.

Full history
Until you pick a month the page shows every change. Pick the month you last played to keep only what is new to you. The date is shared by every item page.
Valve’s patch notes record no changes to Mithril Hammer since patch 7.06d (mid 2017). It works the way you remember.