My 1st death was by a boulder trap ( doesn't count as a mob, does it?)
And my 2nd death was in the marble biome, I REALLY had no idea what the f**k have I found, I was grappling around and then I was turned into stone( I had no idea from what back then) and fell into lava and died. Later on I figured out its the medusa that can turn you into stone, so it seems my 1st death was from her :0
Besides that, I haven't died to anything till EoW( killed EoC on the first try too). I got stuck in the effing worm every single time I tried killing it!
And yes, this was expert.