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Good day,
I have a problem quite annoying, install several mods between them "AliensVsPredator" and "Avatar Mod 2: Out of the Iceberg", but not quite good, the AliensVsPredator goes well but you can not generate the mobs in Creative mode and Avatar mode Mod 2: Out of the Iceber can not unlock skills, does anyone know what this is? 
This could be a bug in the mod or a incompatibility with your mods.
I think you'll have more luck to find a solution for this by contacting the mod creator.
The forge version used on Aternos is v14.23.5.2807(you can see this in your server log) right now, this is the latest available version, as you can see here: http://files.minecraftforge.net/
Make sure that the forge version on your client is also the latest version.
If both is the latest the mod creator is wrong with his assumption that forge is outdated.
I do not think it's Forge, I feel like the server will deny me the generation of mobs
As I said, we can not really help you with mod related problems.
