The Green Talisman can be found in the north of MAP25: Catacombs: Ruined Temple (Strife) near the fountain, behind a wall and some crushers. Oddly enough, you must activate the broken pillar like a switch to reveal the Green Talisman.
This quest item was added in the 2014 The Original Strife: Veteran Edition. Collecting all 3 (Blue Talisman, Green Talisman, Red Talisman) grants a permanent super strength power-up and the Berserk Reborn Achievement.
Note: This item cannot be found if the player is following the Bad Ending path.