After you complete mission 9 (Lost Woods to retrieve the dragon research), you will open up the second half of the game where you have to revisit the levels and take the 'B' path to fight a harder boss and collect talismans to progress in the game. When you beat the boss of the B route for the first time you will earn the talisman for that level. To get this trophy then you must first reach the midpoint of the game, and then beat any one level's B route.
The easiest B route is probably the lvl 18 Medusa in the Ancient Temple Ruins. Not only is it the lowest level 'B' boss, its also a very short route to get to the boss. The Medusa fight is fairly standard you just need to use a lot of air attacks to hit her, and watch for her eyes to glow yellow as that means she is about to unleash petrify - turn away from her to avoid this attack. The next easiest B route and boss is probably the Cyclopes in Wallace's Underground Labyrinth (lvl 20). Ultimately, you need to finish all of the talismans anyways (for the trophy and to progress in the game), so its not a huge deal precisely which level you get this trophy on. See my solution for Talismaster trophy for a tips on beating any of the nine level's B routes.