Might I recommend one of those plugins that disables vertical mouse movement externally?

https://www.doomworld.com/idgames/utils/misc/novert

I know it's being used for Doom here but I *think* it can be made to work with other Dos games.

lcpowell,
If you want mouse look, what you are asking is not really possible. Apparently Build's takes the "analog_moving" data, that is generally assigned to MouseAnalogAxes1, and translates that into "Aim_Up/Aim_Down" data when you toggle the Mouse_Aiming value on and off (by pressing the "U" key).

I think MouseAiming was supposed to force it on by default, but setting that to 1 doesn't seem to do much, as you still have to press the U key once. After that, Blood seems to remember the setting indefinitely, or until you press U again.

I guess you could un-assign the Mouse_Aiming after it's set, that way you wouldn't accidentally toggle it off again.
Mouse_Aiming = "N/A" "N/A"

MagitekAngel,
If you simply want to disable vertical mouse movement entirely, you can tell Blood to ignore any imput by doing what lcpowell did and null out the setting for MouseAnalogAxes1. No additional software is necessary.
• MouseAnalogAxes1 = ""

Go to your game folder: Galaxy > Games > Blood

There is a file called "Launch Settings".

Double click, go to: Controller Setup > Setup Advanced Controller Options > Advanced Mouse Setup

Highlight Y-Axis and press delete.

When you exit, make sure to save. You will no longer move when the mouse moves.

Thank you

If you find the up and down movement is too fast, then you can lower the sensitivity of the Y axis making it less of a pain.

Settings\Controller Setup\Setup Advanced Control Options\Advanced Mouse Setup\Mouse Y Axis Scales\