There's only one way to get this achievement: be cheap!
You're going to have to constantly SAVE and spam enemies.
Here are some tips to get the job done:
1. SAVE CONSTANTLY. After every felled enemy, before every boss battle and especially after/at the beginning of each stage to retain the least amount of damage possible. If you screw up, reload your save.
2. Memorize the location of thieves (little gnomes). If you know you can get potions from theives up ahead, don't be afraid to use what you have. If at all possible, hit thieves and leave potions on ground. Then attack the boss with magic and pick up the potions to attack him again.
3. Spam with beasts. Each beast in the game that you can ride is very powerful. If you practice, you can avoid being hit by relentlessly using them against enemies and even keep your beast all the way to the boss. Use them on the boss without mercy. Dragons work the best.
4. Charge! Charging an enemy can surprise them and get them down on the ground quickly. It also works against bosses and while riding beasts. Just quickly press forward TWICE (double tap). In one quick motion, tap forward, then again holding it forward on your second tap. You will run toward your opponent where you can then hit the attack button for a headbutt if you're the Dwarf or jump kick if you're the Amazon.
5. Who's the best fighter in the game? The DWARF! Use no one else! Trust me, it seems unlikely, but he's the best!
6. When an enemy rushes toward you, jump toward them and rapidly press attack to create a wide range of attack for you to swing your axe into their forehead. Axe? Because you're using the DWARF!!
7. Use the "Zig-Zag Technique". This is most important tip of all. In most arcade-style 2D beat 'em ups, the zig-zag technique is when the player moves up and down the playfield to get an enemy shaken from a direct path toward them. As the enemy gets closer to the player and finally does line up with them, the player can unleash a flurry of attacks. The next time you need to get away from an enemy, use the zig-zag technique to gain an advantage and turn the tables on them!
8. When you start a "new game", do this achievement the easy way and give yourself custom 5 lives and continues.