Damp Powder
OOC: You made the save (and no, you don't have disadvantage on saves, only ability checks) Narrator and I agreed that allowing greenflame blade to ignite kindling would be okay. Either way:
Guyver fumbles about in the dark struggling to follow the draft. Eventually, he stumbles into a doorway, completely by accident. He follows a hallway until he reaches another chamber. Smelling no black powder, he arranges the charcoal, and manages to get a fire going. As he sits, warming his body, and drying himself and his gear, he takes in the surrounding room in the flickering firelight.
The room is small, small enough that the firelight reaches all corners. Along one wall, is a door, and next to the door, a counter with a window. On the counter, an ancient inkwell sits next to a board with a spring operated clamp on one end. Tiny fragments of decayed parchment are still caught in the clamp. Facing the counter is a chair, on swiveling wheels. Cabinets line two other walls. All the furniture seems designed for people almost two feet shorter than you, though the ceilings are high.