Here is the full list of all 12 CLASH - there are Battle Arena achievements.
Complete the Tutorial.
Win a match on Novice difficulty.
Win a match on Intermediate difficulty.
Win a match on Expert difficulty.
Don't lose a single round in a match on Expert difficulty.
Complete a match with a friend.
Win or lose every round in a PvP match.
Win a round where you have taunted.
Win the match after losing 4 rounds in a row.
Win a match by Ring Out.
Win a match by Time Out.
Taunt at least 10 times in a single round.