Mouse acceleration is one of the things we don't get to fiddle within Mass Effect Legendary Edition options but thankfully, there is a limited workaround for this issue.
Mouse acceleration is a highly disrupting mechanic that really needs a toggle option in every new game these days as it ruins the players' muscle memory for any other game where they might be used to the same mouse sensitivity at all times.
In the case of Mass Effect Legendary Edition, this is not an option but the players have found a workaround, for the most part. Unfortunately, it only works in Mass Effect 2 and Mass Effect 3 so you will still have to endure the negative mouse acceleration whenever you zoom in while chasing Saren.
As for the ME2 and ME3 parts, go to the Legendary Edition installation folder to start. If you got ME: Legendary Edition on Steam, just find it in your library, right click, go to Properties and then Local Files on the side. Click Browse from the new card and you will be in the necessary folder.
From there, navigate through the following folders:
- ME2 or ME3, depending on which you are fixing
In the Config folder, you will see GamerSettings file that you should make a copy of and move the copy to a different folder. After that, open the file with Notepad and find the [SystemSettings] line and add UseMouseDampening=FALSE underneath it.
As we noted previously, this workaround is only for ME2 and ME3 and, unfortunately, the first game doesn't have a way to turn the aiming modifier off.