Lightning is one of many spells. It requires level 10 to unlock, and costs 30 mana to cast. At higher levels, it increases damage, duration, and frequency. It's a bunch of blue and white lightning strikes, but takes a second to start.
At level 1, Lightning's base damage is 50. For every point of intellect, it deals 1 more damage.
At level 6, Lightning's base damage is 360. For every point of intellect, it deals 7.2 more damage.
With enough cooldown it can be cast twice before the first spell ends, and both versions will do damage.