Here is a hack for Balloon Fight which changes the graphics of the levels and of the enemies to those from the game Joust.
Balloon Fight (JU) [!].nes
CRC32: A0DABE0A
MD5: 04855CD998B41C56C22CE451B1879A05
SHA-1: BE2C30D69B1EBA76EAF1CC259DFA41F0F29B0FB2
SHA-256: D10749D1A94FA28350C23973CFE95879367CCB553802DAA4CC3434ACABB446E4