Fungal Frenzy

You can do this achievement during the Therazane daily Fungal Fury. It takes place on the Crimson Expanse, on the east side of Deepholm. Without spoiling too much, you need to have unlocked the Therazane dailies to do this achievement.

It's rather straightforward once you know what to look for.

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• Poolstool: Red Mushroom, a bit larger than the others. Gives you the debuff Poolstool. Increases damage done by 50%, but increases damage taken from all sources by 100%. Lasts 2 minutes.
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• Shuffletruffle: White mushroom, very similar to Ghost Mushrooms. Gives you the Shuffletruffle debuff. Increases run speed by 50% and decreases attack speed by 30%. Lasts 2 minutes.
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• Shrinkschroom: White with a brown center. Gives the debuff Shrinkshroom. Reduces size by 50% and speed by 20%. Lasts 2 minutes
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• Trapcap: Purple with red dots. Explodes when you click on it, dealing around 3500 fire damage and knocking you back quite a distance, with potential fall damage. Be careful, you can get knocked into a hostile mob, and triggering the explosion near a neutral mob will cause them to aggro you. This is the only one that won't give you a debuff, so it needs to be triggered last.
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A good strategy is to scope the place out, find where the various mushrooms are located, and then do them all quickly in succession. Remember to save the Trapcap for last! 2 minutes should be more than enough time to get this done.

PS: I wrote down what each mushroom looks like because currently in the beta, all the mushrooms are named 'Sprouting Crimson Mushroom'. This may or may not be intended.

Good luck!

Do not go into the water it will clear your buffs.

Ok here is how I did it
the Shrinkshrooms is over on the Left side of the map
Shuffletruffles on the right side of the map,
Poolstool are by water,
Trapcaps are by the red crystals, simple as that.