Decided to accept the challenge and give it a go!:
Rook - The Last Bastion
Innate: Hold The Line
Passive: While Rook is within 500 range of a tower, both the tower and Rook will take 15% reduced damage.
Active: Rook can target an allied tower within 500 range of him, melding him into the tower. He assumes control of the tower for up to 10 seconds, and can target any enemy within the tower's attack range. While commanding the tower, 20% of all incoming damage to the tower gets redirected towards Rook's health bar instead. If Rook is currently at, or falls below 5% health, he cannot command a tower and/or he is ejected from the tower.
Cooldown: 180 seconds (Not affected by Cooldown Reduction)
First Ability: Landslide
Active: Rook slams and rips up the ground in front of him, dealing 60/110/160/210/260 (+0.5 Attack Damage, 2.0/2.5/3.0/3.5/4.0% Rook's Maximum Health) physical damage to all enemies caught in the line skillshot. The ground under the skillshot becomes unstable for 6 seconds, slowing enemy's movement speed by 20/22/24/26/28% while they are on it.
Cooldown: 15/13.5/12/10.5/9 seconds.
Mana Cost: 80/75/70/65/60 mana.
Second Ability: Stoneform
Passive: For every 25 armour Rook has, he gains 5/7.5/10/12.5/15% base health regeneration. For every 25 magic resist Rook has, he gains 5/7.5/10/12.5/15% base mana regeneration.
Active: Rook turns his skin to stone, reducing incoming damage by 34/40/46/52/58% for 3.5 seconds and increasing incoming healing effectiveness by 12%. He cannot basic attack or cast spells during this time and moves 20% slower.
Cooldown: 24/23/22/21/20 seconds.
Mana Cost: 50 at all ranks.
Third Ability: Seismic Roar
Active: Rook roars loudly, targetting the ground in a cone in front of him. The ground is ripped up and shredded, damaging and affecting enemies caught in the roar. Enemies within 200 range of the roar take 80/125/170/215/260 (+0.4 Attack Damage, 5% Rook's Maximum Health) physical damage and are knocked back to 250 range away from Rook. Enemies between 201 and 450 range of the roar take 60/100/140/180/220 (+0.25 Attack Damage, 3% Rook's Maximum Health) physical damage and are slowed by 50% for 1 second.
Cooldown: 15/14/13/12/11 seconds.
**Mana Cost: 65 at all ranks.
Ultimate Ability: Unrelenting Fortress
Active: Rook's body becomes stone and moulds into a giant bounder. After a 0.5 second delay, Rook charges in a straight line as a boulder. Any enemies hit by Rook take 100/175/250 (+0.35/0.40/0.45 Attack Damage, +3/5/7% Rook's Maximum Health) physical damage and are knocked aside. After being knocked aside, enemies are stunned for 0.75 seconds. Rook will end the charge at the end of his maximum range or if he collides with a wall. As he rolls past, he leaves behind a trail of unstable ground that slows enemies on it by 20/24/28%.
Cooldown: 110/90/70 seconds.
Mana Cost: 110/100/90 mana.