Magic Resistance is a stat that modifies the amount of magical damage taken by a unit. Magic Resistance values can be modified by items, hero abilities, leveling units and alliance bonuses. A positive Magic Resistance value reduces the amount of magical damage a unit takes while a negative value increases that damage.
Magic resistance has no effect on physical damage or pure damage.
Modification
The following have a positive effect on Magic Resistance values:
Cloak
Hood of Defiance
Pipe of Insight
Age of Chivalry- Knight
alliance bonus - Scaled
alliance bonus - Mega-Scaled alliance bonus
- Viper's ability Corrosive Skin
- Anti-Mage gaining a level
- Terrorblade gaining a level
The following have a negative effect on Magic Resistance values:
- Mage
alliance bonus 
Bracers of Desperation
