it probally is worth more then 20
I bet if yu keep it for a few more years it will be worth a lot more
Yes, it is- to a collector. That bill needs to be inside a special protective case. Contact your local numismatic agency and they'll be able to assist you. There is one mule-star $20 from 1934 currently going for $175 on EBAY... I've seen them go for more.