The Arena is a cool ‘sealed draft’ style sub-game. For 150 gold you get to pick one of 3 randomly allocated heroes, then make a deck from 30 single selections from 3 cards. Upside is you don’t have to worry about playing George Osbourne who’s spent 5000 quid on his deck of legendaries with custom ‘prole-skin’ card-backing.
It’s a good way to get extra free gold too.
You keep playing until you lose 3 games. The more you win, the better the rewards. You always get a new pack of cards AND you get between 1 and 4 randomly determined other freebies t00 (depending on how you do).
While it’s 50 more gold to go into the Arena (than straight out buying a pack of cards) its normally pretty easy to win 3 games and make yourself break even. If you push on PAST 3 wins you can get quite nicely ahead.
My best outside of Beta was 6 wins, and for that I got a 100 gold on top of the pack.
It’s actually fairly easy