South Sea Bog Hogwarts Legacy Merlin Trials are required to achieve 100% completion in the small swampy region. Solving the South Sea Bog Trials, along with the rest available in Hogwarts Legacy, will unlock you the Merlin’s Beard! Trophy/Achievement.
However, to start solving Merlin Trials, you must first complete the Trials Of Merlin main quest and get your hands on some Mallowsweet Leaves. You can find Mallowsweet Leaves in the open world or even grow them yourself at a potting table in the Room of Requirement back in Hogwarts Castle.
For the latter option, you must first buy the Mallowsweet Seed Recipe from The Magic Neep in the Hogsmeade village. It’s also worth mentioning that while solving Merlin Trials, you complete Challenges that can get you inventory size upgrades, which can be claimed from the Exploration tab of the Challenges menu.
Where To Find the Two South Sea Bog Merlin Trials in Hogwarts Legacy
On the South Sea Bog map below, I have marked the locations of the two Merlin Trial puzzles. As you can see, one is in the center of the swamp, and the second is on the southern side.
Merlin Trial #1: In the Middle of Some Leafless Trees
The first South Sea Bog Merlin Trial is found southeast of the South Sea Bog Floo Flame in the northern part of the region. Once you reach the first location pinpointed on our map, you’ll see the Trial’s altar in the middle of some leafless trees. Interact with the altar to start the Trial, for which you must bring three groups of green fireflies to three stones with green dots. The rocks are close to the altar.
For the first stone head southeast of the altar, and the closest group of fireflies is behind a fallen tree further to the southeast.
You have to get very close to the fireflies, then cast Lumos to make them follow you back to the stone. The second stone is northeast of the altar, and another group of fireflies is under a big tree across the water further to the northeast. Use Lumos again to guide the fireflies to the stone.
For the last stone, you have to go west of the altar, and the remaining fireflies are southwest across the water, under another big tree. Upon bringing the last fireflies to the remaining stone, you complete the first Merlin Trial in the South Sea Bog region.
Merlin Trial #2: South of a Medium Bandit Camp
The second South Sea Bog Trial is south of a Medium Bandit Camp in the southern part of the region. Go to the location on the map above and start the Trial by interacting with the altar. Then, look southeast of the altar to spot three balls on three pillars, as shown in the following screenshot.
Destroy the balls with basic attacks, then go northeast of the altar and pass the machine to reach the cliff’s edge. Now look down to see another three balls on three pillars. Repeat the process and destroy the balls.
Then head north of the altar and drop down to find the last three balls you must destroy next to the polluted pond. After you destroy the last ball, you complete the Trial.