Different MP cost for same skill on two different characters.

Pretty much all scenarios are covered in the example I provided.

For Mana, pure Percentage skills, and other misc. stuff use the following:

<pre>{{#expr: BASELvVALUE+((MAXLvVALUE-BASELvVALUE)/(MAXLv-BASELv))*({{#var:i}}-1) round 0}}</pre>

All you literally have to do is '''replace''' the BASELvValue, MAXLvVALUE, MAXLv, and BASELv. You don't have to do any math. The wiki does it for you.

For your Mana cost issue, you can just do the following:

<pre>{{#expr: (BaseMP+((MaxLvMP-BaseLvMP)/(MaxLv-BaseLv))*({{#var:i}}-1))/WeaponMPMultiplier round 0}}</pre>

The WeaponMPMultiplier depends on your weapon. For spears, it could either be 1.05 or 0.95 depending if the skill is physical or magic.

For Independent Atk skills use the following:

<pre>{{AbsoluteDamage|{{#expr: (BASELvVALUE/INDEPENDENTATK)+(((MAXLvVALUE-BASELvVALUE)/INDEPENDENTATK)/(MAXLv-BASELv))*({{#var:i}}-1) }}|1}}</pre>

For Hybrid skills, combine the two with a plus sign between them. Just don't mix up the fixed values with the percentage ones. BASELvVALUE for percentage parts are not the same as BASELvVALUE for fixed damage parts.