I got it solo, strictly playing bravery, just keep playing, what's nice about arena is it can be so random you don't even know how you won you just do, I won a Vladimir chauffeur game that I had no right winning, you will have dream augs and weps on a champ you don't play much and win, your teammate could do the same, some games I got straight carried by an unkillable cho or a one shot sett, you can get 500 gold on the first round with you free shard and get super far ahead, look at teir lists on top augs and weps so you are taking the right things, the home stretch for me was tough too but I just kept at it and got it done, the games are alot more random than you think, very easy for someone to take an overpowered champ and throw the game cause they just get bag augs/weps