Full Synchronisation Requirement - Do not take any damage
Chase after the Templars, turning to the left and climbing up into the opening in the cave wall. Keep following the path and holding down the sprint and high profile buttons the whole time. Use the hookblade long jumps when you can, but focus on not falling or getting hit by the stray shots from the riflemen. After Ezio almost falls, go through the doorway and keep climbing and jumping. Eventually you’ll get to some small pillars and structures just above the rapids, be more cautious when crossing them to avoid leaping into the water. Remember to long jump on the hanging flower pots and lanterns, then turn left and climb over the wall. Go down the following zipline and head over all the short gaps.
Now the Templars will have the bright idea to start throwing barrels of gunpowder your way. Jump across the ruins of the bridge and keep heading forward, using long jumps with the hookblade when you can to avoid having to take more lengthy detours. Take the last zipline near the waterfall to end up above them, and air assassinate your way onto the boat. After the scene, immediately back away from the approaching guards. Try and use bombs or ranged attacks to take them out before they get close, even blocking attacks can sometimes deal damage to you and thus ruin your full synchronisation. If you’re confident in your counters and execution streaks, feel free to just patiently wait for the right moment to take them all down, but be careful not to ruin everything after your hard work getting through the chase scene!
After you take them out, open the six chests and then use Eagle Sense to find the hidden door on the adjacent wall. Inside you’ll find another statue and the third Masyaf key!