Skills:
Melee-increases up close combat skills.

Frontal-increases skills of spearman, cavalry.

Ranged-increases skill of ranged units.

Teamwork-increases skills for every unit, greatly increases skills of ballista, catapults, ice dragons, trebuchets.

Riding-increases riding skills of riders, turning speed, speed, so forth.

Taming-greatly increases skills wild animal riders, all animals but horses.

(More to be added)