Magus, Demon of the Seas.
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Basically, Magus functions as a mid-range Control Mage that focuses on luring people into her sphere of influence and then devastating them with stackable CC and damage that racks up over time.
Recommended Build:
Optional: 
AA range: 500
PASSIVE 1: Surging Tides Every 15 seconds, Magus gains bonus effects on a basic ability. This passive has a 30% reduced cooldown in the river. PASSIVE 2: Siren’s torment Magus suffocates opposing champions when they are hit by her spells. Once the breath gauge hits zero, champions are stunned for 1/1.25/1.5 seconds. Breath gauge recovers by 10% per second if they have not received damage from Magus for 3 seconds.. This passive has a cooldown of 15 seconds per champion.
Q – Water Pulse: Cooldown – 10/9/8/7/5 seconds Cost – 50/55/60/65/70 mana per orb Magus fires an orb of water that travels 500 units or explodes on the first target hit for 60/90/120/150/180 + 50% AP. Can be charged up to 3 times. The orbs deal AoE damage at 60% efficiency in a 150 unit radius. Water pulse reduces enemy Breath gauges by 15% each. **Enhanced Water Pulse: **Magus can dash 100 units either left or right per orb thrown. The orbs must be cast within 1 second of each other in order for Magus to dash.
W – Riptide: Cooldown – 20/19/18/17/16 seconds Cost – 80 mana Magus conjures a riptide spanning 400 horizontal units. Enemies attempting to move in the direction opposite to the riptide move 95% slower, but receive a 20% buff when moving in the correct direction. Enhanced Riptide: Riptide increases to 550 horizontal units and grounds enemies.
E – Deep pressure: Cooldown – 22/20/18/16/14 seconds Cost – 30/35/40/45/50 mana per second Magus swirls a field of water around herself in a radius of 400 units; submerging enemies in a forceful current, dealing 5/10/15/20/25 + 8% AP damage per 0.5 seconds over 5 seconds. Each tick of Deep Pressure reduces enemy Breath gauges by 7% each. Enhanced Deep Pressure: Enemies are slowed by 30% when caught in Deep Pressure.
R – Song of the Deep: Cooldown – 105/95/85 seconds Cost – 130 mana Magus enthrals enemies with her alluring sonata, charming them for 1.5/2/2.5 seconds and dealing 150/250/350 + 55% AP damage upon cast. Song of the Deep affects all enemies caught within its cone AoE.
