Thread: Skill lvl ups

i think there is a probability list on aigis wiki, just same skill name, if you use same unit then both unit cost can be reduce and skill level up

Originally Posted by http://millenniumwaraigis.wikia.com/wiki/Unit_Combination#Skill_Level_Up

A skill level-up may occur during Unit Combination if one or more material units used:
- have the exact same skill name and skill tier as the receiving unit (you may use multiple of these units in one combination); or
- is Christia, Spirit of Rainbow (you may use only one of this unit per combination).
When attempting a skill level-up, the first skill level up is guaranteed, but successive level ups will have a diminishing success rate. However, when using Christia, Spirit of Rainbow, the chances of a successful level-up is higher than it would be when attempting to level-up by units with the same skill.
More here

For 5-level skills, same-skill skill-ups have a 100%/50%/25%/5% chance on 1st/2nd/3rd/4th increase. Christia skill-up chances are 100%/75%/50%/25%

Edit: Saki'd