unityplayer.dll
This file is not a system component: supplied with the game by its publisher. Restore it from the source that installed it rather than downloading a replacement.
Do not download this DLL on its own
Searching for a missing DLL by name leads to sites that hand you that single file. It is one of the oldest and most effective malware delivery methods there is, and a system DLL from an unknown source is indistinguishable from a deliberately modified one. There is never a legitimate reason to obtain a runtime component that way.
What it is
The Unity engine runtime. It ships inside each Unity game folder rather than being installed system-wide, so every game carries its own copy and its own version.
Where you see it: A Unity game failing to start after an interrupted update, or after antivirus quarantined a file.
Verify or repair the game files through the launcher: Verify integrity of game files on Steam, Verify on Epic, Repair on the Xbox app. Check your antivirus quarantine as well, since UnityPlayer.dll is a frequent false positive. Copying a UnityPlayer.dll from another game will not work, because the version has to match the build.
Why there is nothing to download here
There is no verified download we can offer for this one, because installing a file is not the fix. The steps above are what actually resolves it. That distinction matters: the sites ranking for this file name are selling a download that would not have helped even if it were safe.