The Chosen Ones

LIGHTNING PROTECTION - ULTIMATE ABILITY
Description: Fradz draws energy from the sky and combines it with his mana to create a powerful lightning shield and a lightning ball (hovering on top of him). The shield nullifies all incoming damage during its duration.
Enemies attempting to attack/target a spell on Fradz will be hit by a blue/red lightning bolt from the lightning ball, dealing damage to them. When the spell expired, the resulting flash blinds enemy units in a 400 AoE (missing 80% of attacks in the next 5 secs). The spell lasts 10 seconds on all level.
Effects:

• Activation: Monsoon Effect.
• The Shield: Mana Shield Effect + Lightning Shield Effect in WC3.
• The Ball: Here

Calc:

• Blue Bolt: damage based on Magical Bonus, Spell Level (Aero will do this   ).
• Red Bolt: 1.5xBlue Bolt damage.

Icon: Here
EDIT: Add some small details:

• Fradz's attack damage will be reduced by 30% when the spell is active.
• Mana cost should be 250+lvl*50.

RE-EDIT: Simplifying.