To start this quest, you must complete the first quest by Tim the Wizard. The quest is just defeating a champion Dreadroot. Once that is completed, various quests/tasks will open up.
For this quest, talk to Izzy the Imp. Complete his quest and the achievement should unlock.
*** Spoiler - click to reveal ***
You are looking for material to defeat THE Dreadroot. Izzy has the Cool Stickers that you are looking for. However, he will only give it up if you can help him with a task. Sunflowers have been putting out his fun forest fires. He wants revenge.
Follow the cookie smell. The bar will increase the closer you get to the location. The location should be near a RV site/campsite off to the upper right. Vanquish the nearby enemies. Dig up the cookie to realize that it was the wrong chocolate chip cookie.
Follow the new cookie smell. It will be on the path to the Z-Tech Factory. Vanquish the nearby enemies and the sun spot and dig up the cookie pile. The cookie was Oatmeal Raisins, so we definitely found the wrong cookie.
For the last time, follow the cookie smell. Defeat the Champion Sunflower and its sun spot and dig up the cookie pile. However, it was a Garguatian named Cookies that we were looking for.
Escort and Protect Cookies through the factory. Once outside the factory, a tree will spawn and toss Cookies out of the world. You must become the Cookies now and vanquish the Sunflowers in the nearby area.
A Sunflower Queen will appear. During the fight, she will charge up her royal beam. During this time, destroy the sun spots to prevent her from charging up. She will repeat this every quarter of her health. Also during the fight, she will spawn sunflowers to heal her. Prioritize vanquishing the smaller sunflowers because they can heal her back to full health quickly.
Turns out she will release her ultimate move and have seemly unlimited sun spots to destroy. All hope is loss... until Cookies comes back to save the day! The quest is over, you will receive your Cool Stickers, and the achievement should unlock!