The sovereign debt crisis in the Eurozone evidenced the shortcomings of EU financial supervision and regulation. It was the ECB's pledge to do "whatever it takes to save the euro" restrained contagion. It is the ECB's newly gained role in prudential supervision that should provide a guarantee of stability. Yet, did the ECB have the power to act as the safeguard of financial stability in the Eurozone? How far do its newly-acquired powers extend? In this article we explore these issues, to try and delineate the limits to the ECB's mandates and competences, and the interplay between those. We conclude with an analysis of the limitations that may arise if the ECB's powers on prudential supervision were to clash with its monetary policy mandate.