These are how to get the two achievements in the new Sifu update that are secret.
How to Obtain Secret Achievements (New Update)
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I won’t be covering the other achievements, as they are all very straightforward and easy to obtain.
Bonus Stage
Earn this achievement by selecting the “Car Club” arena. Simply beat up the blue car right next to where you spawn, until the achievement pops.
Beatmaker
Select the “Showtime!” Arena Challenge, clear the first zone. In a room adjacent to the room with the zone you just cleared, will be mixing equipment – the same mixing equipment from the arena’s menu image.
Roll across this multiple times to get the achievement.
You can get the Fighter in the Pond achievement in Bellowing Mountains (Dragon arenas, second to last section, requires 56 stamps to open).