Mo Creature's Thread:
1.
Forge Client (adfly) direct(tested with Forge 6.6.0.497)
2.
GUI Api 0.15.2-1.4.6
3.
CustomMobSpawner 1.11 Mirror
Please make a backup of your minecraft.jar file and then:
1. install Forge (unzip the .zip file and add all of its contents to your minecraft.jar file)
2. install GUI Api (just copy the .jar file into the /coremods folder)
3. Delete the META-INF folder in the minecraft.jar file
4. locate your .minecraft/mods folder
5. copy the MoCreatures.zip and CustomSpawner.zip files inside your \.minecraft/mods folder
6. Play
You can watch this video explaining how to install the mod v4.5.0. (thanks to TheGofa)
And this one that explains how to set up a server with Mo'Creatures 4.4.0 (no changes for 4.5.0)