Hi guys !
For this achievement you'll need to beat the last stage without taking any damage on Knight or Epic difficulty.Obviously it's better and easier on Knight difficulty.It's the only hard level to beat on no damage but,like the others,it's quite easy with the Shield squire.
Start the level with your pet at lv2 if possible to get 2 shields at the beginning and get a full stock of Energy and Squire Energy Potions.
The bosses are not so hard if you know the patterns.Just take your time.Use your Energy Potions if you really want to make a quicker fight and Squire Energy Potions if your loose all your shields.Use the Specter Crossbuster (which is unlocked after beating the game on Epic difficulty) to make this cheevo a lot easier.
Between each battle,wait for your energy gauge goes max then start the next battle,it will save a potion.
There's my video to show you the pattern of this stage (sorry it's missing a boss,my Upload vid exceed 5 minutes,so it cut my 1st battle):
Good luck,have fun and don't hesitate to comment my guide if you have any questions ^^