Rayman Legends

A very easy level to get this achievement is on Creepy Castle - Invaded, which unlocks in the Teensies in Trouble gallery as you progress through the 20,000 Lums Under the Sea gallery.

From the very start of the level, kill the first Toad you see and jump in the water. As you exit the water, you're wall jumping over another Toad and he will fire at the wall, ricocheting and killing him as long as you don't land on him. you can then just run forward and kill yourself on the exposed blade ahead.

The Toad is literally 8 seconds into the level so it takes no time at all to unlock the achievement just repeating these steps.

I was able to do this long before unlocking an invasion level.

Go to world: 20,000 Lums Under the Sea
Hop into painting: The Mysterious Inflatable Island

The very first spot you come across a laser toad and a light camera, you will see a fire hydrant. Its very easy to get it here after you learn the right angle. As the light from the camera moves away from the toad, swim under the toad and sit right at the spout of the hydrant. When the toad shoots swim over the bolt and back behind the toad. The bolt should bounce off the hydrant and back to him. (It may bounce a few times)

The best part is that the checkpoint is right before you see this toad, so its very easy to just restart sequence and do it again.

The key here is to find a toad with an electro-gun next to a flat wall, so his fireball will bounce straight back at him. There are probably a dozen good places to do this, but here was my fastest path to this achievement:

World "Toad Story"
Level "The Winds of Strange - Invaded" (unlocks very late in the game)

About 8-10 seconds into the run you will come to a toad with a gun standing on a big vine. Immediately jump over him and hug the right wall. The best way to avoid the shot AND the shadow-Rayman is to perform 2 wall-jumps, then jump to the left of the toad to avoid the shot after it bounces off the wall.

Once the shot hits the toad and kills him, restart the level and repeat. Once you get to 10 total ( you probably got this to happen a few times naturally through the course of the game) the achievement will pop!

------- Edit -------

If you haven't unlocked the invasion level listed above yet, another great level to farm this achievement is "Mansion of the Deep" (3rd painting in the 20,000 Lums Under the Sea world). There are a bunch of frogs with guns here, and many are near a wall or object where their shot will bounce back at them

here is a simple solution to this achievement.
credits for achievement hunter