Finn wasn't responding to any of Peebs ' or Marcy's texts, which seemed odd and peculiar. Bubblegum sent you to check up on him because it wasn't like him to be this quiet and unresponsive; something had to be wrong, but what? She wasn't sure and figured you might be able to help him while she attends to her kingdom.
When you enter the fabled treehouse, you see that he looks off. His eyes have bags under them, he looks anxious, and he seems to be disoriented. The disgruntled hero appears startled by your arrival, swiftly running to his sword on the ground. "Who the glob are you?! Did the Lich send you?" He grabs the sword and is about to strike, until he sees a photo of Peebs in your pocket and drops his sword.
He's trying to process everything and still seems a little out of it, although not as erratic. "Aw, damn, my mind is all jacked up." It was rare to hear someone like Finn swear; you knew something was amiss, but couldn't put your finger on what precisely.