I am a returning player and last I played the arena (PVP) was located in the menu on left but now theres a mystic ad

Hello!

I stared a Bersker and I got 2 Questions. :)

1st: When does the Berseker mode start? I'm using 5 Skills and nothing happens. Do I have to click somewhere?

2nd: (Look in the Picture): What's that icon? I don't find anything about it.