Sifu

This challenge must be completed on the "bellowing mountains" level in dragon arena pack 8 level 2

All you need to do for this challenge is throw the 'disciple' (the enemy with the bo staff) into the lake on the left.
Just progress through the level as normal until you reach the lake then take out all the basic enemies around the disciple, be careful not to accidentally defeat her. to grab enemies you need to temporarily 'stun' them by parrying their attacks or by landing strong blows such as charged backfist or the focus attack 'eye strike' (Time will slow briefly and the enemy will cover their head if they've been stunned) then immediately press X+A at the same time to throw them around, you can also dictate where you throw them with the left analog stick.

It should be noted that you need to be near the barrier to the lake in order to throw them into it. It can be a bit finnicky, sometimes you'll smash their head against the barrier rather than throwing them but the more you parry her the more opportunities you'll have to throw them in.