This part of the Elden Ring Guide is dedicated to the fight against the Ulcerated Tree Spirit.
Here you will find tips and a video that will help you defeat him as well as information about the rewards you can get.
Rewards: Golden Seed + Banished Knight Oleg Ashes
Location: Fringefolk Hero’s Grave (West Limgrave)
To defeat this boss, which is very similar to the creature you met in the War-Dead Catacombs (but much more powerful), you will have to take its blows with a shield, even if you are a mage. So be very careful and wait for an opening to place a jumping attack. Repeat this operation until you can inflict a critical hit on the Boss when he falls to the ground. After that, move as far away as possible to avoid the creature’s sacred area attack before resuming your undermining work. Stay focused, avoid being too greedy in your attacks and you may be able to defeat it, even with a slightly sub-level character.