Here is a screenshot from a PAK2-enabled client:
One of the enemies in the picture would be visible even without the PAK2 cheat, but the other would not. You can see him right through the solid walkway. Also, either of these enemies might be carrying the Ring of Shadows and would still show up fully visible, rather than as a tiny pair of eyes.
More screenshots are available here.
This is actually just one instance of a more general "PAK2" modification. Some "PAK2" mods do not abnormally increase player visibility, but just change the appearance of objects. As long as it doesn't let you see through walls or see invisible players, we consider it OK. There are also legitimate uses for files called id1\pak2.pak which do not involve model replacement or any other kind of cheating... for example, if you frequently play on servers that requires extra maps or models, you can put the server-specific pak files in id1\pak2.pak, id1\pak3.pak, etc.
Do not ask me for a copy of this PAK2 cheat, or any of its variants.
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