[Champion Concept] Remortem! Herald of the end

Note: The idea behind this champ concept is an assassin that doesn't rely upon burst damage, but upon DPS. The kit is packed with fairly little burst, but a many tools to deal damage over time and a means of surviving long enough to deal that damage. While this kit will have high dueling potential and a bit of team fight potential with a DoT, this champion will quickly fold under focus fire. And with low base damage and high scalings, it's unlikely that this champion will find much success outside of building glass cannon.

I think this should go without saying BUT. ** All numbers are subject to change** I'm no expert on balance and it's possible I tuned them too high or too low. I'm posting this hoping for feed back on how viable the kit concept is than on whether I've got the numbers too high or too low.

ReMortem

Assassin/Fighter

The end is coming, and he is it's herald.

A force unlike any other is approaching Runeterra and it's herald has arrived. He sows death where he glides and his eye is always watching. Beware the shadows, for he can be anywhere.

Passive: Mordebit: Basic attacks and Q mark targets for 5 seconds. Upon a target reaching 4 stacks, they take physical damage equal to 25/50/75/100% of ReMortems bonus AD.

Q: Confodere: ReMortem flings a shadow from his sword in a straight line skill shot, striking the first tartet hit and dealing damage to it and up to two enemies within 300 range of the first target, marking all three. This ability can crit. Range: 700 Mana: 80 Cooldown: 12/10/8/6/4 seconds Physical damage: 10/20/30/40/50 (+100% Bonus AD)

W: Tempestatem: Toggle- Remortem surrounds himself in a deadly field of energy, dealing damage to all enemies within range of himself and increasing his Base Health Regen and Base Mana Regen for every enemy damaged. This regen boost is only active while enemies are being damaged by Tempestatem. Range: 250 Mana: 20 per second
Physical damage: 10/15/20/25/30 per second HP Regen: +5 per target damaged MP Regen: +2 per target damaged

E: Fulgur: Active- ReMortem dashes a short distance, passing through any obstacle on the way. If he passes through an enemy champion, he gains a temporary shield granting him damage reduction for a short duration. Auto attacking while the shield is active will increase the duration of the shield by .25 seconds. Range: 300 Mana: 100 Cooldown: 15 Duration: 4 seconds Shield: 15/20/25/30/35% Bonus AD Damage reduction: 15/15/20/20/25%

R: Finis: ReMortem dashes through nearby target champion, dealing damage to them and marking them for death. Each auto attack for the next five seconds adds a seal to the mark, causing it to deal damage over time during the marks duration, seals max out at six. Range: 400 Mana: 120 Cooldown: 120 Initial damage: 25% current HP Damage per tick per seal: 10% total AD Maximum potential damage: 250% total AD