Mortal Shell - Martyr's Blade & Both Winterglass upgrades

Where to find the two-handed greatsword, Martyr's Blade, and it's both upgrades, the Petrified Winterglass and the Radiant Winterglass. I will also demonstrate the use of the weapon and the abilities.
Mortal Shell was released Aug 18th 2020.
I received a free copy of the game from Playstack.
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