To unlock this achievement you will need to complete the fifth mission called "Spirit of the Forest".
Platforming is a bit different in this level due to traps and the place falling apart. No big deal just keep moving forward.
Fighting occurs a bit more then previous levels however still poses no real concern. The enemies use rifles and projectiles but nothing too hard. There is no "boss" fight to speak of.
You will also unlock the "Used Leos special move" achievement early in this game. Master Splinter will once again tell you when to use it.
Below is a walk through for your reference.