How to complete the Alchemy: Miracle Growth side quest in Tiny Tina’s Wonderlands

You can find the Goblin right outside the kelp you need to bypass to progress the story, preventing you from entering Wargtooth Shallows. Speak with them, and you’ll receive the Alchemy: Miracle Growth side quest. Upon receiving the quest, you’ll need to test out the potion in some nearby kelp. It won’t be the one blocking your path. Instead, turn around, and interact with the kelp next to the coral rocks. After interacting with it, it’ll become a rock, and you report your findings to the Alchemist once more.

The Alchemist will report that he needs a unique ingredient to perfect the potion. You’ll need to find it at a nearby dungeon, which you can find amongst a small pile of kelp behind you. There shouldn’t be attacked by anything on the way to the dungeon, but expect plenty of fighting when you get there.

Proceed inside the dungeon. You’ll need to beat two waves of enemies blocking your path. Upon beating the final wave, a chest will appear, and you’ll find the final ingredient for the potion, and you’ll leave the dungeon. Return to the Alchemist to present them with the last ingredient, and you can then destroy the kelp blocking your path, proceeding to the next quest.