Separate library from content
Apotheosis provides gameplay systems, while Placebo supplies shared infrastructure used by supported releases. Downloading Placebo alone does not install Apotheosis. Likewise, installing a content mod without its required libraries can stop the loader before gameplay begins.
Check the selected release
Use the dependency list for the exact Apotheosis file you want. Confirm Minecraft, loader, Placebo and any other required libraries together. Requirements can change across release lines, so an old tutorial or a different modpack is not a substitute for the selected file's details.
Install and verify as a set
Put the compatible runtime jars in the same intended instance and launch the matching loader profile. If a dependency message appears, follow its requested range. For server play, use the administrator's pack so you are not combining independently chosen client files with a different server setup.