Skills only affect the army the hero is traveling in. The only exception to this is logistics; which affects the whole campaign.
Leadership
Level 1
Level 2
Level 3
+10%
+25%
+45%
Increases the amount of units in an army able to attack at the same time.
Logistics
Level 1
Level 2
Level 3
+10%
+25%
+45%
Speeds up army movement within a valley.
Pathfinding
Level 1
Level 2
Level 3
-10%
-25%
-45%
Speeds up army movement in cities.
Scouting
Level 1
Level 2
Level 3
+10%
+25%
+45%
Increases hero's line of sight.
Knowledge
Level 1
Level 2
Level 3
+5%
+10%
+20%
Speeds up the hero's experience gain.
Defender
Level 1
Level 2
Level 3
+10%
+15%
+25%
Increases army defense.
Archery
Level 1
Level 2
Level 3
+10%
+25%
+45%
Increases attack power of ranged units.
Fighter
Level 1
Level 2
Level 3
+10%
+25%
+45%
Increases melee units' attack power.
Calvary
Level 1
Level 2
Level 3
+10%
+25%
+45%
Increases cavalry attack power.
Ballistics
Level 1
Level 2
Level 3
+10%
+25%
+45%
Increases the attack power of machines.
Healer
Level 1
Level 2
Level 3
0-20
0-40
0-80
Revives a number of troops after returning from a campaign.
Artificer
Level 1
Level 2
Level 3
25
30
35
Increases the amount of artifacts the hero can store. Also, reduces upkeep coasts of non "one time use" artifacts.
Ranged Cavalry
Level 1
Level 2
Level 3
+10%
+25%
+45%
Increases ranged cavalry attack power.
Multiple Heroes[]
Only three heroes with the same skill can be effectively used in an army.
The first hero uses the skill at 100%,
The second hero works at 60%,
The third hero works at 20%,
Note: Any additional heroes have no effect.
For instance, If you have three heroes in an army with master archery, the archery bonus is better than with 1 hero. However, it is less than 3x the bonus. if you add another hero with master archery, it will make no difference.