Why Sersi? I didn't know her untill yesterday. She was on the list on a website and her name did ring a bell [but only slightly] so I followed the link. I red about her and saw her and her powers, then I remembered she was in one of the prelude comics to the Marvel Heroes. Her powers would be enough to do a suggestion for her but she actually sounds as a cool hero. On some of panels I use here for references you can see some of this but now: Ladies and Gentleman. The stuning, the transmuting, Eternal Mistress of Illusions [drumroll] Sersi!

Sersi

Introduction

Early Years
Sersi has existed for many years, although she seems to be considered one of the younger Eternals. She was still a child during Giglamesh's reign as champion-king of Uruk.

Circe
It is known that she encountered the Greek hero Odysseus during his 10 year journey home known as the Odyssey. She turned Odysseus' companions into pigs, but Odysseus, who had been given a magical herb by Hermes, resisted her witchcraft. Circe fell in love with Odysseus and transformed the pigs back into men. After they stayed on the island for one year, they left to continue their voyage. As Circe she also imprisoned all the evils that escaped Pandora's Box.

She was present during Nero's burning of Rome and was assisted by Makkari. She also assisted Merlin during the days of King Arthur Pendragon.

Modern Era
In modern times, Sersi lived on the Upper West Side in New York City when the Fourth Host of Celestials arived on Earth. Ikaris left Margo Damian in her care while he went off to defend the city against the Deviants' attack. When he was captured, Sersi alerted the other Eternals, but was captured herself by Kro's forces. She was released when a truce was reached and was part of the group who revealed the races' existence to Professor Samuel Holden.

Avengers
Sersi became associated with the Avengers after inviting them to one of her parties, and meeting her long-lost "cousin" Starfox of the Titan Eternals. She started a flirtation with Captain America (much to his embarrassment) and assisted him on a few cases. When her fellow Eternal Gilgamesh was injured in battle and could not longer function as an active Avengers, Captain America invited Sersi to join the team in Gilgamesh's place. Sersi accepted

For more go to Marvel Wikia

Powers and skills

As an Eternal of Earth, Sersi is descendant from the original Eternals created by the Celestials and further empowered by Kronos's experiments with the cosmic life-force.

Near-Immortality: Eternals like Sersi possess total conscious control over their molecular structures, which are reinforced by cosmic energy. As a result, they are virtually immortal and indestructible. They only age when they choose to, and are virtually invulnerable to any force weaker than their own cosmic energies or total molecular disintegration.

Matter Transmutation: Sersi is able to transmute nearly any item or being into almost whatever she wishes. She is 'adept level 5', the highest level an Eternal can reach in such categories.

Illusions: Sersi is skilled in the use of illusions. Her illusions affect all five senses and are virtually indistinguishable from the 'real thing'. She is considered a Class 4 of 5 Eternal when it comes to her skill at illusion-casting, with only Sprite known for sure to be more skilled than her. Sersi's illusions are so effective, it's often difficult to tell whether she is employing illusions or her matter-rearranging abilities.

Sersi is superhumanly strong and being able to lift 20 tons but also can slap Hercules with enough force for his head to turn.
Regenerative Healing Factor: On the rare occasions Sersi is physically harmed by some extreme force, she can heal herself using her molecular control powers. Sersi once reconstructed her own arm after it was disintegrated by a Deviant weapon.

Telepathy: Sersi can psychically communicate, read minds, and project her thoughts into other people. She can compel the distracted or weak minded to do her bidding through hypnosis.
Telekinesis: She can mentally move and manipulate objects, living creatures, and fly.
Cosmic Energy Projection: Sersi is able to project blasts of cosmic energy from her hands or eyes, in the form of light, heat, or concussive force.
Teleportation: She can teleport herself and others across vast distances although doing so is unpleasant for Eternals.

Skills:
Sersi is an accomplished fashion designer, often using her powers to make changes 'on the fly'. She's a graceful dancer. Sersi is lingual in many ancient/dead languages, having lived through the time they were spoken. More impresively, possibly by telepathy, she knew Kree language.

Power Trees

Eternal
Sersi as an Eternal besides being immortal and invulnerable have few powers shared among her kind in different capacity. She is a telepath and a telekinet. Her powers of illusions are one of the best in her kind and that means a lot. Sersi can fly and project cosmic energy from her hands and eyes.
Transmutation
What Sersi is the best in is Transmutation. Turning enemies into trees or into their own enemies is done with ease. Mosters turned into trees, weapons turned into monsters fighting their owners, air desitegrated to suffocate enemy or water turned into cube of alloy that traped inside a god. This and much more is in her aresnal.

Sersi deals three types of damage and have summons. She have two energy powers [Eye beams and Energy bolt] Five physical powers, Three Mental powers and Few summon powers. Her talents let you change things a bit so she have more of mental or energy powers etc. Another thing is her offensive passive which also helps with this.

Alternatively like with Mister Fantastic, powers could deal whatever type of dmg is needed and apropriate talents would be there to support that even further.

Again as with Mandarin tags for "Area" powers can be wrong but it all depends on hero and builds so it would be fix by people who do the numbers :)

Eternal

Energy bolt Basic, Ranged lvl 1

Send a green bolt of energy into your enemies.
Medium-fast single target
Dmg X

Dash Movement lvl 1

Envelope yourself in cosmic energy and dash through enemies.
Dmg X

Ground throw Ranged

Using telekinesis reap a chunk of the ground and throw it forwards hurting enemies.
Dmg X
Vulnerable
Small cooldown. 3s?

Eye beams Ranged

Pretty powerfull show of force.
Fast attack speed single target [not barrage because each one have to look strong]
Dmg X

Mind Control Summon

Take controll either of one strong enemy [yellow] or 3 weaker minds [blues/grays].
They can change areas with you but if you go to hub they are disbanded.
Hp X
Dmg X

Lift and slam Ranged, Area

Using telekinesis you lift enemies from the ground and slam them into it.
Dmg X
Weaken
Small Cooldown. 3s?

Snakes Area

Create illusionary snakes that are real enough to bite enemies and slow their movement.
Dmg X 2/s
Slow
You can have up to 3 areas of snakes.

Flying Travel

As most Eternals Sersi also can fly.
Travel Speed 1000

Scimitars Ranged

Realistic illusions of scimitars apear near you in the air and after short deley they fly into target enemy cutting anyone in the line.
Medium-Fast attack speed [if channeled 3 scimitars hover near you, when one flies another apears].
Dmg X to the target
Dmg X to enemies in the path - less
Dmg X 2/s bleed to both the target and enemies in the path.

Army Summon

Ilusionary soldiers apears in target area to do your bidding. 4 melee and 3 ranged. Sometimes they are swordsman and bowman. Sometimes they area rifleman and futuristic swordsman. They don't leave area around their spawn [screen size] and disapear after a time or when you use them again.
Hp X
Dmg X
They deal mental dmg

Transmutation

Friend is Foe Area lvl 1

It's easier to let them take care of eachother.
Works like confusion but visually change half of the targets into other enemies.
+Dmg

Your inner monster Summon

Mutate one enemy into hulking beast of a mutant that starts fighting for you until he dies.
Hp X
Dmg X
Hp/5 in hubs
You can have only one monster.
Monster retains enemy affixes.
Maybe some visuals of the original?
Example of a beast Sersi spawned and then mutated:

Check your guns Ranged, Area

Enemy weapons, clothing, body parts turn against them. Changeding into tentacle creatures full of teeth and spikes they start attacking their masters. VFX tentacles.
Enemies are unable to attack for Xs [fear/stun?]
Dmg X 2/s
After Xs weakend [lack of guns etc]
Small cooldown

No air for you Ranged

Desintegrate air around single targets head for Xs to deal dmg from suffocation. Doesn't work against robots.
Dmg X 2/s

Preparation Area

You can change anatomy of you and your allies to better fit the situation no matter if it's creating gills to go under water or hardening their skin.
Buff in area around you.
+Dmg, Defense, Crit, Hp/5, Spirit/5 for Xs
Cooldown.

Giant Hand Ranged, Area

From the ground bursts giant hand hitting enemies and throwing them away and on their backs. Hand crumbles after hit.
Dmg X
Knockback then knockdown.
Vulnerable
Cooldown

Cube Ranged

First time it was made to hold a god. There is no hope for you.
Create a hard syntetic cube out of air around your target. He is trapped and takes dmg from suffocation. Enemies that were near the target are pushed away from him as the air is turned into the cube.
Dmg X/s
Stun [disable movement and attacks]
Can't be hurt or directly targeted.
Small cooldown

Lizards Summon

They are lizards, they should be lizards.
Change up to 5 enemies in an area into lizards that fight for you for a time. After that time they turn back into enemies who are dazed for a moment.
Cooldown.
One instance of lizads can be active.

Pigs that you are Signature, Area

You shoold look the part. [Spidey calls dibs on the ribs]
Turn gray and blue enemies into pigs [small hp nonviolent enemies]
Thos who can resist your power [yellows and up who survive the dmg] still take dmg from the changes that tore their insides and their bodies. VFX enemy is violently and painfully shapeshifting.
Dmg X
Cooldown

Ultimate

Every trick in the bag

Cosmic Hulk got this treatment but I was stopped by Ikaris before the last trick.
First create few explosions in the air like balls of fire. After that create two monsters out of the ground [stone bridhead spewing flames, yellow pudding tentacle monster grapling and slowing enemies]. Turn target enemy into stone [irresitable petrification] and unleas your eye beams at him. When the petrification ends giant sword spikes him from the air. Was it illusion or transmutation we will never know.
Dmg X - fireballs
Dmg X 2/s - fire bird and burn
Dmg X - tentacle attacks of pudding monster
Dmg X 2/s - eye beams
Dmg X - giant sword
Monster stay a while longer after the sword.

Talents

Defensive
Mistress of Illusions
+Dodge, Deflect
5% Chance that projectiles will go through you. After they pass through they can hit only enemies not heroes.
5% Chance that melee attacker will get confused and will attack nearby enemies for Xs with +Dmg. Cooldown on this Xs
+Hp as eternal
+Hp/5 a lot as transmutation.
When you go bellow 20% hp regenerate X Hp instantly, X hp in 5s and gain +X Hp/5 for Xs.
When defeated stand up again because you area immortal Xs cooldown.

Offensive
Cosmicly imbued Eternal
Offensive Traits: Energy, Inteligence
+Crit and Brut Dmg
Physical dmg +X% dmg to non summon illusion powers
Energy dmg +X% dmg to illusion summon powers [maybe there should be one more?]
Summon dmg +X% to energy powers
Mental dmg +X% to energy powers and +X% to summon powers

Balance of those "X"'s would be important if this is the chosen model.

Talent Examples:

Eye beams become basic power loosing dmg and Energy bolts isn't basic and gains dmg
Scimitars become basic power loosing dmg and Energy bolts isn't basic and gains dmg.
Scimitars you create 7 scimitars in front of you and launch them in a cone damaging everyone in the area. Slower attack, Dmg X, Dmg X 2/s bleed.
Eye Beam channeled piercing power. Dmg X 2/s. If changed to be a basic power Energy bolts pierce enemies dealing half of it's dmg as dmg over 3s [VFX green "elecitric" lines surounds the body]. Every enemy behind the first get's less dmg.
Lift and Slam Become a Telekinetic wave You create a curved wall of force that you send forward and it becomes higher and wider [cone]. Dmg X, More Dmg further the target. Knockback in the 1/3 cone from you Knockdown in the remaining 2/3. Mental dmg.
Ground Throw Instead of a line your throw piece of ground into the target area.
Ground Throw becomes Bolder Throw To make your illusion more real you interact with it. Pick up a giant bolder and throw it at enemies. Mental dmg.
Snakes Snakes come from under your feet and attack outward. Small area of effect and 7 snake groups [on ground projectiles] that going outward chase enemies to bit them and slow them. Dmg X area, Dmg X snake group. Small cooldown.
Snakes become Eye Blast Shoot target area with energy from your eyes. Dmg in target area 2/s.
Your inner monster becomes Deage and Devolve you change your enemies into weaker versions of themselves. They decrease in size, loose X% hp and X%dmg. or if this is too breaking [because every party could want that extra debuff] - Dolls You change enemies into little dolls. You grow bigger for a second and stomp on them. Then you and them get back to your regular selves. Melee dmg X. Allways crits. This also could just be another power.
Check your guns becomes Floor spikes Medium attack speed. Ground in front of the target enemy is turned into a long spike that pierces him. One comes back after the second one is beginign to shoot out from the ground.
Check your guns becomes Personal explosives You change enemies weapons, clothing, body parts into granades that are attached to them. All enemies in target area get separate explosion after 1s of using this power. It deals X energy dmg and leaves enemies weakend. 1/s or 2/s attack speed.
Giant hand becomes Piranha plants Bitting piranha heads with long necks spring from the ground biting enemies, leaving them bleeding and vulnerable. Field doesn't last long and you can have two of them. No cooldown.
Giant hand becomes Car crash Two illusory cars ride from oposite sides of the screen and meet in the middle exploding. Mental dmg. Dmg X low - drive through. Dmg X explosion. Cooldown.
Lizards Dmg X in an area - if someone would be bellow 10% hp after that he is changed into a lizard that stays in place and vanishes after Xs unless it's killed [it have low Hp]. Cooldown.