Got bored, solved combo.
There are 3 variables to take into account:
#orbs
skill %
skill level
With 0 orbs, Combo always does nothing.
Otherwise,
total % = floor(skill % + (#orbs - 1)*(skill level/6))
For example, with level 23 combo, 3 orbs: (117% on skill)
% = floor(117% + 2*23/6) = 124%
One interesting thing to note is that with level 1 Combo, it always does 100% damage (any # of orbs). So really a level 70 Crusader just gets flying orbs around him, no damage boost. lol.
EDIT: Advanced combo is affected by a little more:
#orbs
combo skill %
a.combo +%
For orbs 0-5:
total % = floor(combo skill % + (#orbs - 1)*(skill level/6) + a.combo%)
For orbs 6+:
total % = combo skill % + 20% + a.combo % + 4*(#orbs - 5)
This is true regardless of level of combo/advanced combo, always 4% per orb.
There are 3 variables to take into account:
#orbs
skill %
skill level
With 0 orbs, Combo always does nothing.
Otherwise,
total % = floor(skill % + (#orbs - 1)*(skill level/6))
For example, with level 23 combo, 3 orbs: (117% on skill)
% = floor(117% + 2*23/6) = 124%
One interesting thing to note is that with level 1 Combo, it always does 100% damage (any # of orbs). So really a level 70 Crusader just gets flying orbs around him, no damage boost. lol.
EDIT: Advanced combo is affected by a little more:
#orbs
combo skill %
a.combo +%
For orbs 0-5:
total % = floor(combo skill % + (#orbs - 1)*(skill level/6) + a.combo%)
For orbs 6+:
total % = combo skill % + 20% + a.combo % + 4*(#orbs - 5)
This is true regardless of level of combo/advanced combo, always 4% per orb.

