UPDATED for forsaken Masters: https://www.youtube.com/watch?v=Is3JbtRRZUs
One thing I love about Path of Exile is that it really punishes players who don't prepare properly for it's challenges. The Act 1 boss Merveil is the perfect example of this - characters who who fail to get their gear in order before the fight are in for a frustrating series of deaths (especially melee characters who can't dodge the ice attacks). In this video I go a bit overboard on the preparation but it serves to highlight how easy the fight can be if you set yourself up for it nicely.