The Overlord mod gives you the ability to conjure and convert an army of skeletons to rule over and fight for you. There are three types of skeletons you can raise: Baby and Warrior skeletons are grown in Skeleton Makers, while Converted Skeletons are created by right-clicking existing skeletons with golden apples after splashing them with weakness potion.
You’ll need an Overlord Stamp or Seal to rule them first though. The stamp is one time use and the seal is unlimited, so you’ll fair better with a much larger army with the seal. These will be necessary to be sure your skeletons will obey you. Check the forum link and you’ll find step by step instructions on how to create skeletons as they require 16-32 bones, milk and optional armor.
You can feed your skeletons milk to level them up by right-clicking and placing milk bottles in their inventory or throwing the milk bottles at them. They’ll need more the higher level they get. Or they will naturally level up via XP after battles. And you can heal them using milk as well.
And to be sure your skeletons are safe in the daytime or even just disguised as more human-like and non threatening, you can craft a skin suit for them and they won’t burn up in the sun.