Polymorphing while wearing crystal plate mail, leather armor, or iron mail can cause you to merge with the armor and turn into that respective material of golem (glass, leather, or iron), with the armor returning unbroken when you revert back to your normal form.

Rock piercers instakill stone golems, glass piercers instakill glass golems and iron piercers instakill iron golems.

YAFM for when polymorphed into a glass golem and you rub a touchstone against “-“.