This hack reduces the random battle encounter rate in Vay and Vay Unworked.
There are multiple patch files included as well as a Python-based patch program.
Each patch file divides the battle rate with a certain amount.
Apply the desired rate file - the bigger the number - the smaller the encounter rate - or use the python patcher.
Vay patches are in .ips format for 2048 byte/sector and 2352 byte/sector image files.
Vay Unworked patches are in .xdelta3 and .ups format due to the changes being moved into an offset 16MB in the image files.
Vay (USA) (Track 01).bin:
File/ROM SHA-1: E2C9D8438CEF364D31D7FFEE2DF5894E09168572
File/ROM CRC32: 1D9BE2B9