Brainf_ck: I bought Fresh Supply because I was told that I would also be able to play the original game. I installed OUWB via the game extras but nothing happens. How do i start the original game?
DustyStyx: If you tried installing it through Galaxy, it doesn't actually install OUWB for you, it just downloads the installer. Check to see if there is a file named ouwb_windows_1.21.zip in your GOG Galaxy\Games\Blood - Fresh Supply\!Downloads folder. Unzip the setup_one_unit_whole_blood.exe installation file and install it with the exe.
Once you have it installed, you [should] be able to find the "One Unit Whole Blood" icon in your start menu or in C:\ProgramData\Microsoft\Windows\Start Menu\Programs\One Unit Whole Blood [GOG.com]
When you click the OUWB icon, this will launch an instance of DOSBox and give you a menu where you can select 1 for Blood or 2 for Cryptic Passage. You can also go into Game DOS Settings to change your keybindings, but you can also change these in windows by editing blood.cfg (found in the installation directory) with notepad, under the [KeyDefinitions] section. Just make sure to make a backup first.
If you need to toggle mouse look, this is the "u" key by default.
If you find the default BUILD mouselook a tag janky, you might find BMouse to be helpful
bMouse 0.5 - Mouse driver that fixes the terrible mouselook on DOS Build games