So, I've deiced this game needs two characters:
1) A Voodoo Witch Doctor.
2) A mage with no mana, so instead they use health (like Tryndamere and Dr. Mundo).

Yeah, it's not an in-depth suggestion, these are just basic concepts that I'd like to see implemented.

Witch Doctor is still in the works I hope

As for #2 Yeah yeah Heroes with just health...blah blah blah BORING!

How about a female summoner/mage similar to Viegar except all mana (sorta further explanation following)

Name: Ethereala
Background: Once a strong rivalry existed between Veigar and Elendra, two major forces of magic one of dark and one of light. Veigar could manipulate the dark forces like none other but in Elendra he found a rival one whose mastery of the force of light were like nothing he'd seen. Elendra and Veigar had many skirmishes which resulted in many a scarred battlefield. As time passed both grew in their power til Veigar found a way to banish light altogether, or so he thought, Elendra received the challenge from Veigar who was more than ready for her. Elendra tried her best to match or overcome Veigar like the past battles but to no avail Veigar maliciously cast the light banishment spell on Elendra not knowing what lay dormant within her. A bright flash of light and a huge explosion resulted in a change in Elendra, No longer possessing a pure corporeal body made of flesh and bone but that of light amplifying her powers to overwhelm the darkness. Veigar tried numerous times to defeat Elendra learning that something Ethereal you cannot truly destroy only slow down immensely. Elendra became Ethereala the being of pure magic and light.

Attack: Low
Health: Very Low (Ethereala has NO Health at all not being Corporeal)
Armor: Very High (Ethereala's armor is that of pure light nothing but the strongest blows can penetrate her being, Though she is susceptible to magic being made of it she isn't as magic resistant as Corporeal beings)
Magic: Extreme (Ethereala's magic powers surpass anything ever seen, so strong she can lay waste to hundreds of minions)

Note: Due to the nature of this Hero Ethereala has absolutely no health but instead channels damage through her Ethereal matrix that makes up her body instead sapping away her mana which is not only for casting spells but her lifeblood. All physical damage is filtered through the light armor dropping it by 50%, Magic Damage is Taken at 100%

Q: Bring the Light
Rank 1: Deals 100 (+0) Magic Damage in a Cone in front of Ethereala Cost: 100 Mana
Rank 2: Deals 150 (+0) Magic Damage in a Cone in front of Ethereala Cost: 200 Mana
Rank 3: Deals 200 (+0) Magic Damage in a Wider Cone in front of Ethereala Cost: 350 Mana
Rank 4: Deals 300 (+0) Magic Damage in a Wide Cone in front of Ethereala Cost: 400 Mana
Rank 5: Deals 500 (+0) Magic Damage around Ethereala Cost: 550 Mana

W: Focus the Light (Toggle)
Passive: Ethereala's Armor and mana regeneration rate is highly increased granting her x% more armor/50% more Mana Regeneration.
Active: Ethereala gives up her massive regen and x% (+100 magic dmg) Armor for a heavy targeted blast of light that damages the target for x% of their health
Rank 1: 25% More Armor/50% Regeneration; 10% of target health Cooldown 2 min. Cost 100 Mana
Rank 2: 35% More Armor/50% Regeneration; 20% of target health Cooldown 1:40 Cost 200 Mana
Rank 3: 45% More Armor/50% Regeneration; 30% of target health Cooldown 1:20 Cost 250 Mana
Rank 4: 50% More Armor/50% Regeneration; 40% of target health Cooldown 1:00 Cost 400 Mana
Rank 5: 75% More Armor/50% Regeneration; 50% of target health Cooldown 1:00 Cost 500 Mana

E: Beacon of Light
Ethereala focuses a beam of light in a target location revealing the map in that spot for x amount of seconds.
Rank 1: 5 Seconds Cost 100 Mana
Rank 2: 8 Seconds Cost 150 Mana
Rank 3: 10 Seconds Cost 250 Mana
Rank 4: 12 Seconds Cost 300 Mana
Rank 5: 15 Seconds, Also reveals any stealthed units Cost 400 Mana

R: Solar Eclipse
Ethereala Charges up for 3 seconds to unleash a wave of solar energy damaging minions, champions and non base turrets for x amount of damage.
Rank 1: 500 Damage Cost 750 Mana Cooldown 5 Min.
Rank 2: 750 Damage Cost 1200 Mana Cooldown 8 Min.
Rank 3: 1000 Damage Cost 1500 Mana Cooldown 10 Min.

The ultimate is like it is due to keeping her just powerful enough to be a serious threat but not Uber OP by someone spamming the ultimate every few seconds, and on Rank 3 keep in mind that Ethereala's difficulty to play and master is hard as all heck due to her having nothing but Mana which Rank 3 would sap about half your full mana bar.

Appearance brilliantly white and bright with flowing hair like the morning sun and a flowing dress the color of the sunset. Corporeal Appearance same but much much duller colors.

Thoughts? Comments? OMGWTFBBQSAUCEOP??
CHANGES MADE! Check it out!

It's kind of funny considering the lore you gave that veigar's ult would one-hit this champ every time.

Edit: Oh and I just realized that a single giant's belt would probably turn her into a tank, if she has 1000 armor, then she'd now have 750hp (150 natural + 500 giant's belt) and an expected damage absorbtion of 8250hp. (11x750) not much worse than a mid-late game tank with 3000 health and 200 armor.

I said if you didn't like it you could change it So feel free to alter anything I was just throwing down something off the top of my head and as for lore If RIOT would be so darn kind as to flesh out Veigar's REAL story I might not have to BS one....

Sorry If I sounded like I was shooting you down, having a hero with almost entirely mana instead of health is a cool idea, just some things that came to mind. You do have very original ideas with alot of potential.

It'd be better if she just didn't have any health, and that her mana bar functioned as a health bar I think.