Here's an elite-skeleton and a skeleton-mage.

Elite Skeleton:

Health: 650 Strength: 65 Armour: 30 Dexterity: 70 Defence: 75 Luck: 2

Primary Job : train

Attacks: Sword(lvl1) Armor (lvl5) Lightning (lvl10)

Attracted by : 3x3 training and 1slab prison

workshop skill : 1

research skill : 1

Skeletonmage:

Health: 500 Strength: 55 Armour: 20 Dexterity: 70 Defence: 75 Luck: 2

Primary Job : train

Attacks: Fireball(lvl1)Fire Bomb (lvl3) Heal (lvl4) Armor (lvl5) Missile (lvl7) Lightning (lvl8)

Attracted by : 3x3 training and 1 slab prison

workshop skill : 1

research skill : 1

Credit Clint Bellanger
https://opengameart.org/content/skeleton-warrior-0

please read the instructions of my other custom creatures, it's always the same. (inside creature.cfg they are called "skele" and "skelemage"