Any ways to increase magical damage

[Arcsol]

I was wondering if there was a way to increase damage done by spells somehow, more specifically by percentages. I looked at the Runed Bracers (which reduces spell damage by 33%) and it also has Data - Magic Damage Increase... so my questions are:
1) Is there a way to increase spell damage?
2) Does the runed bracers skill increase magical damage done or recieved?
3) If so, will it work with triggers like "Cause Unit to damage unit"?

I guess that's all, and now that I'm asking about magical damage, can I stack the damage reduction if I have for example multiple Runed Bracers?

 

[MortAr]

1. I think if you put a negative value (-XX) it will increase it instead of reducing it.
2. The runed bracers REDUCES the damage, meaning if you take 100 SPELL damage, you will take 33% less of that damage
3. It doesn't matter how the damage is taken, but, if you use "Damage type Spell" it will be count as a spell-damage.

 

[Arcsol]

1. I think if you put a negative value (-XX) it will increase it instead of reducing it.
2. The runed bracers REDUCES the damage, meaning if you take 100 SPELL damage, you will take 33% less of that damage
3. It doesn't matter how the damage is taken, but, if you use "Damage type Spell" it will be count as a spell-damage.

Runed Bracers has two Data values, Damage Bonus and Damage Reduction. A negative value may work, but more as a debuff than a buff. I wanted to know if this "damage bonus" will work on both a triggered spell damage and a common spell damage, but I still don't know if this skill works for sure

 

[VestriDeus]

I tried doing something with that early (Trying to make a certain type of unit take extra damage from spells), but with runed bracer's ability, you can't put a negative value; it defaults to 0.00