WARRIORS OROCHI 3 Ultimate

In Gauntlet Mode you have to try and find the correct portal so that you can escape. The longer you stay in the level the harder it gets. The portals I find that leads to the escape point are towards the edge of the map rather than the ones littered around. (Whether this is constant on all levels is yet to be proven) Early on it can be quite hard after it surpasses level 10 Miasma. So if you are not high levelled try and find the exit as soon as you possibly can. Once you hold LB on and it tells you it is the escape point, then hold LB once more for about 5 seconds and it will tell you that you are victorious. The achievement will unlock on the post battle screen.

The other solution gives you the gist of the idea but there's a little more to it. Once you enter Gauntlet Mode, you'll go through a level in which you should run to the blue circles uncovered on the map and hold LB until a brief cutscene reveals it's the escape. Hold LB again to finish and it will bring you to camp. Continue back to Stage Select and enter the highlighted panel. You'll have to repeat this process twice consecutively for the achievement to pop and if you die, you'll start the first of the two again. A key is to avoid fighting by double jumping over enemies or running around them. You can also attack while holding LB on the Dragon Portal to fend off the enemies as it registers.