It sounds like this mod implements scaling, which I don't like. Does it only apply to the creatures that the mod adds in, or does it apply to the original creatures as well?

And what does the read me mean by you shouldn't merge this mod with Creatures? Is Creatures another mod?

The author tell us not to include this mod while merging (with TesTool) and also tell us to load Creatures X after merged objects.esp

Scaling applies to all creatures (if I understood the readme well).

Huh? So load after mashed list? And I merged creature x with everything else in wrye mash... What do I do?

No: merged objects.esp is a plugin, while mashed list.esp is another one.

Load order should be like this:
- Other mods
- Creatures X.esp
Then, you merge objects with TesTool excluding Creatures X
Thus, you will obtain the Merged Objects.esp plugin

Then with Wrye Mash you adjust load order as follows:
- Other mods
- Merged Objects.esp
- Creatures X.esp

Then with Wrye Mash you need to create the levelled lists including all plugins.
Then, always with Wrye Mash, you adjust load order as follows:
- Other mods
- Merged Objects.esp
- Creatures X.esp
- Mashed Lists.esp

Now clean you savegame with Wrye Mash (or, better, start a new game) and play!

Whoa, sounds confusing. I have a question about always loading creature x last. It seems like it conflicts with the lighting mod. Is it possible to load the lighting mod after creature x?