Echidna, the Monster Maiden [Medusa's Sister]

Part of the mythology hero series.
Part of the LORE series, which incorporates hero lore.

Echidna
Type : Agility, Melee, Dire. Carry, Durable, Jungler.

Lore :
The sister of the legendary Medusa, born immortal and beautiful, was captured by masked rogues. Unfathomed by her beauty or her pleas for help, they locked her in a prison deep underground, where a mass of deadly reptiles lay. Unknowing, Echidna was bitten by a hideous snake. As her body slowly died, she saw that Medusa had come to save her. The walls of the prison were shattered,and the unbreathing assailants lie dead on the grount. She saw Medusa's hideous face, but then something dawned upon her. Offering her death or a mortal life as a reptillian beast, she chose life. For that tragic night, she learned that beauty is just an illusion of the eye, but the reality of power never fades.

Abilities
[Q] Deadly Bite [Active]
Echidna lunges at the enemy, dealing damage and healing her for the amount done.
Damage: 50/100/150/200
Cooldown : 13/11/9/7
Mana Cost : 50
Echidna's toxins can cause hallucinations, headaches, swelling, and death.

[W] Reptillian Scales [Passive]
Each time Echidna takes an instance of damage, she gains agility.
Agility gain : 1/2/3/4
Max Stacks : 10
An enhanced reptile ability, Echidna's scales regrow at a rapid rate.

[E] Scale Sheild [Passive]
Echidna blocks damage for each instance of damage equal to a percent of her agility.
Percent : 25/45/65/85%
Echidna's unpenetrable armor of scales has never broken when attacked by even the greatest of swords.

[R] Monstrous Rebirth [Active/Autocast]
When cast or upon dying, Echidna turns into egg form [she can't move]. For each second she is in the egg without it being destroyed, she gains agility. When the egg bursts or is destroyed, she is reborn with full health.
Agility per second : 7/14/21
Egg max duration : 3
Cooldown : 120
Mana Cost : 140/180/220
When in the twilight of battle, Echidna becomes a being of ultimate monstrosity.
Items :
Early Game
Hand of Midas
Power Treads/ Phase Boots

Core
Ethereal Blade
Manta Style

Adding ability lores next.

I think her ulti is a bit OP, even Phoenix's isn't that powerful. Maybe you should reduce the agility gained per second to total agility gained.

Her scale shield too, it should be reduced.

Her E should have a limit.

Otherwise, interesting abilities. But, she's a little to OP.

You can never deal damage to this hero late-game thanks to the armor from agility and Scale Shield. When you have 100 agility, Scale Shield provides an 85 damage block, completely nullifying the attacks of supports in that stage of the game. Once she gets more than 200 agility or 300 thanks to Monstrous Rebirth, she will be unstoppable by anyone who doesn't have 5 Divine Rapiers.

One suggestion is to nerf Scale Shield's percentage damage block to, say 100% at all levels, but add a certain number of attacks before the Scale Shield "breaks", maybe 2/3/4/5. That way, she can't run into 5 enemy heroes and tank their **** anymore, but still retains her super-defensive capabilities.

Other than that, there is not much to say about this hero, except that it is a high-armored auto-attacker that needs to be dealt with using Magic-based damage (eg. Outworld Devourer). Against opponents with not enough spells, I think she would be a terrifying carry.