Pharmacist from Hell 1996 one on netflix

A trio of bad boys comes across some ghosts and monsters. They decide to visit a pharmacist in their town to ask for his advice because he is said to have power to communicate with the spirit world. The mysterious old man says “if you meet ghosts and they attack you, you should show the cards and chant some spell which I will give you…” . Then gives the trio three cards which have odd spells written on them. The boys bravely fight against the monsters following the pharmacist’s instructions, but…! Why do the ghosts and monsters appear only in front of the boys?