Oxidative stress is among the main culprits for the progression of chronic diseases such as cardiovascular diseases, diabetes, and neurodegenerative disorders. It is well known that dark chocolate possesses polyphenols as major constituents which dietary consumption has been associated to health beneficial effects. Consequently, this study aimed to analyze dark chocolate (DC) and dark chocolate enriched with medicinal mushroom Coriolus versicolor (DCC) and hazelnuts (DCH) regarding antioxidant potential and total polyphenol (TPC), flavonoid (TFC), flavan-3-ol (FLA) and proanthocyanidin (PCA) content. DPPH^•, CUPRAC and ABTS^•+ assays were applied for measuring antioxidant capacity. The average of all antioxidant tests for each product was used for calculating the antioxidant potency composite index (ACI). The mean values of all antioxidant assays indicated that all chocolate products contained potent antioxidants. The addition of hazelnuts to dark chocolate significantly affected its total flavonoid content. Regression analysis among results obtained with antioxidant assays revealed that dark chocolate and dark chocolate products may act in mixed mode, by direct reduction via electron transfer or by radical quenching via H atom transfer. Flavan-3-ols had the most significant impact on the ability of the analyzed samples to reduce metals, while proanthocyanidins primarily acted as radical scavengers. The obtained results provided additional information regarding the value-added dark chocolates enriched with bioactive compounds of medicinal mushroom and plant origin.