Level 6
Look at the key area next to Mr. Deer, light a fire on the oil lamp, open the glass cover on the flowerpot, sow the seeds in the butterfly, water with a bucket, cover the glass cover, click to grow a white flower, then click to wither, then click Grow black seeds.
Check the grinder, put the glass back, add the nettle seeds, and grind them to get an unknown black liquid.