a poisonous mist, possibly Miasma filled the air...you had no mask or protection against it, so you covered your nose and continued whatever you were doing... eventually you got fed up, and decided to see what was causing this diseased gas....and once you looked....it was the diseased titan, made during the age of sickness...Regiasma....

Regiasma stood there, emitting tons and tons of Miasma (poisonous gas) staring at you...not moving...