Crazy strong. The only usable summon if you don't cheese by summoning before fights. The AP efficiency is crazy with this one. The skeleton starts with 12 AP which is 300% from your base investment. The skeleton is also very tanky, has a very high accuracy and a utility skill. IMO it offsets the cost just by standing there and taking a beating, BUT it also deals an insane amount of damage for a 4 AP skill if it hits 2+ times. Godly. Compare it to 7AP and 8 AP summons. Yes, they are strong and have good skills, but they often leave your caster without ap and exposed to threats, and are usually worth less than just using a skill yourself. But not this one.

Where can you find this skillbook?

this summon also lasts more turns than the elemental ones