This ability is made entirely in the Data Editor, there are no triggers. When cast, an area of units randomly receive positive or negative charges. After 10 seconds, if any units are within range of their polar opposite (positive is next to negative) the charges will explode with electricity dealing damage to each other and all nearby units.
You might recognize this mechanic from Naxx in WoW. :)
The Custom Unit Spell - Polarity Shift Team
