To rescue Ivo you become Timmy the mouse, get 'Poster' from Fox who is putting them up. Please note: That you have to wait until the fox has pasted the poster in glue before turning it into a 'Rebel Poster' otherwise it will not stick to the chair, as stated below by JasoX FIN.
Get 'Charcoal' from fire that is burning, Mix poster with charcoal to make 'Rebel Poster'. Wait until the knight stands up and put the poster on the back of his chair. He will drop 'Keys' pick them up and give them to Ivo.