Trine 2

So you need the following to do this guide:
Charge (2 Points for Knight REQUIRED)
Ice Arrows LEVEL 2 (3 Points total REQUIRED, the first level arrows won't freeze fully)
Monster Levitation (1 Point for Wizard)

On level 6 you'll want to play the level normally until you reach two fire streams next to a red cauldron. Using the wizard complete the pipeline to have the fire heat the cauldron which generates red lizards.

@@@Switch Difficulty to Hard@@@

Now that your on hard and next to a checkpoint wait til you can get three lizards out as the THIEF. Using her fire your LEVEL 2 Ice Arrows once at each of the lizards. Hopefully they are close and you will not need monster levitation to move them closer together. Now use the KNIGHT and quickly CHARGE through the three monsters. If you charge, PRESS LT, through them in under a second you will get the achievement.

There is infinite spawn here so no worries about having to retry.

This is a fairly simple task, but it can be a little frustrating until you work out the best way to tackle the situation. I recommend that you use the second level frost arrow with the thief, and the charge with the knight. This will cost you 4 points, so you may need to reset your current skills to unlock the required ones.

Once you have these skills in place, head to chapter 6 on the hard difficulty and locate the first caldron. These cauldrons will spawn an infinite amount of enemies, so lure three enemies out and freeze them with your ice arrows. Once you have three frozen, switch to your knight and press LT to charge through them.

When you encounter three or more enemies at once, reset your skills and select Frost Shield (1 point), Charge (2 points) and Monster Levitation (1 point).

Use the knight and block enemy attacks so that they freeze. Try to freeze them near each other, but be careful that the others don't accidentally shatter the frozen ones. If there are archers that don't move by themselves use Monster Levitation and place them near the others. When you have three enemies frozen at the same time use the knight's Charge and shatter them by one quick dash.

There are plenty of opportunities for trying this during the game. There are almost always three or more enemies attacking at once.

Welcome

Here is video guide for this achievement.
Credits goes to NTAGameGuides channel.