This is probably one of the more impressive pieces of dollar bill origami designs that I’ve seen in terms of detail. The creator’s name is Won Park and I found the instructions here: http://www.origami-resource-center.com/support-files/dollarkoifish.pdf
This koi was made out of an American $20 and was part of a school of koi that were a gift my grandmother had asked me to fold for my cousin. Each one took about 2 hours to fold but I think I could have folded them faster if I wasn’t being so cautious to get them perfect.
I really enjoy dollar bill origami because it makes for interesting gifts. I also enjoy seeing a waiter face when I leave some as a tip at a restaurant. The way their face moves from amazement to confusion over whether they should/can unfold it.