The Arenas Expansion Title update for Sifu has 8 achievements worth 350 gamerscore.
Unlock a new arena pack.
Get 3 stamps in any arena challenge.
Clear 25 different arena challenges.
Clear 45 different arena challenges.
Get gold stamps in a Manhunt arena challenge.
Get gold stamps in a Capture arena challenge.
Get gold stamps in a Survival arena challenge.
Get gold stamps in a Time Attack or Performance arena challenge.