Sedna the ALMIGHTY
She's like a healer tank!

Phire's l33th4x guide to proness
this is my guide to using Sedna as a primary healer and secondary DPS/silencer
So basically, with this chick, you chill in the back and heal people until the fight breaks out and then run in and pounce people or silence them to prevent heals/teleports. This requires good positioning so that you aren't within range to be attacked most of the time as you focus on healing your main DPSers to let them dump their damage while you wait to get that last needed DPS for the kill. I never liked summon abilities so I completely avoid her Summon Yeti and minion buff skills. I also never buy idols for even more minions.
General Skill Spec Overview:
Level 1: Heal 1 - Heals 600
Level 2: Pounce 1 - 400 Damage + Interupt
Level 3: Healing Wind 1 (12HP/s Regen Aura)
Level 4: Heal 2 - 900
Level 5: Pounce 2 - 600 dmg
Level 6: Healing Wind 2 (24HP/s Regen Aura)
Level 7: Heal 3 - 1200
Level 8: Pounce 3 - 800 dmg
Level 9: Healing Wind 3 (24HP/s Regen Aura and enemy priests can't heal in your presence)
Level 10: Heal 4 - 1500
Level 11: Pounce 4 - 1000 dmg
Level 12: Silence 1 - Interupts Spells and enemies affected can't cast for 3 seconds
Level 13: Inner Grace 1 (+5% Movement Speed (MS) +10 HP/s)
Level 14: Inner Grace 2 (+10% MS +10HP/s)
Level 15: Pounce 5 - 1000 dmg & +15% MS +15% Evasion Aura for 5 seconds
Level 16: Lifes Child (Heal 5) - 50HP/s if your HP < 30%
Level 17: Inner Grace 3 (+15% MS +20HP/s)
Level 18: Silence 2 - 4 seconds can't cast
Level 19: Silence 3 - 5 secs
Level 20: Magnificent Presence (-7% cooldowns on abilities)
Notes on skills: You can mix up Silence & Inner Grace, maxing Silence first and Inner Grace last if that's your playstyle. I use Silence as a save until I get my pimped out gear because it allows me to silence everyone around me to prevent them from interrupting my heal so I can heal save myself when I am in a bad spot. Other good uses for silence obviously are to charge in and silence the enemy crew you are engaging to spike damage them down, where added silence time could help. I usually avoid this because before I get my items I sit back and heal and run in to pounce people who are low to avoid getting targeted so I can focus on healing everyone else.
Economy & Items:
This section will be a brief idea of how I spend money with Sedna from start to finish.
As soon as the game begins I get the Staff of the Warmage favor item to add max mana for early heals and melee DPS. I also buy as many mana potions as I can afford, usually 5. As soon as I've done that I sprint to a flag to capture and usually it seems a good idea to let Sedna creep solo for quick leveling. If you do pair Sedna up with someone in a lane it should be with a melee class tank type that can whoop some ass while Sedna heals.
If Sedna creeps alone she has to chill back when other Demigods are around because she is SUPER WEAK at the start. All you need to do is hopefully capture a flag and let a few creep waves kill each other to get level 3. Once you get level 4 you can start going around and ganking nearby heros as you see fit, but I usually try and wait until Level 2 Heal before grouping up for ganks.
As soon are you have 4250 gold go buy a Heart of Life. The Heart of Life is one of the best items in the game. The reason is because it will regenerate your health and mana to full as long as you aren't being attacked, and THEN some. Usually as soon as my mana gets too low to heal I back off away from all creeps and hit the Heart of Life to start the mana regen. If I am near someone I can heal I try to heal quick so I will still be back at full mana by the time the effect wears off.
When you have extra money that isn't needed in the war effort I try to buy +armor +hp and +crit items, here are a few I like a lot for Sedna:
Groffling Warplate: 5200 Gold. +675 HP +1200 Armor
Slayers Wraps: 3300 Gold. 10HP/s +30 Damage and 10% Chance to Critical for 2x damage
Duelists Cuirass: 3000 Gold. +350 Armor +500 HP +5% Chance to Critical for 1.5x damage
Platemail of the Crusader: +20HP/s +1000 Armor & 1% Chance on Hit to Heal 300
Journeyman Treads: +400HP +15% MS & Chance on Hit to +50% MS for 10 seconds
With these items at level 20 here are your stats:
5210 HP with 97.3HP/s regen
3484 Mana with 12.8M/s regen
3500 Armor - BEAST!
370-410 Damage HOORAH
You attack every 1.18seconds
So, you crit 10% of the time for a minimum of 740 damage with the Wraps and another 5% of the time a minimum crit of 555. You can max crit for 820 but it seemed to be a 500ish to 700ish crit about every 10 swings or so. 1v1 at level 20 I think shes damn hard to kill due to her heals and mass crits + pounce.
Tactics:
At the very beginning Sedna is super weak and should stay towards the back to avoid being targeted. Focus on healing allies. Use pounce to get that last bit of damage in. If you are in trouble don't hesitate to either silence then heal or start your heal, the sooner the better. Warn your allies that you have to heal yourself so they don't overextend expecting a heal.
Whenever I am low mana I IMMEDIATELY run to the back of the line and hit my Heart of Life and try to heal whoever I can while it's active without getting hit by anything. I figure it has a short cooldown so you should be using this between every Demigod engagement.
Most of the time I sit in the back and let the heavy DPS guys go to work on the target while watching for heals or good silence opportunities. Once I level up and can tank a bit I'll start charging in without tank backup.
Spell Usage:
Pounce has a really short cooldown, so if you have full mana you should spam Pounce as much as possible while still healing allies and not getting too deep in the shit such that you get your shit pushed in.
Heal is broken as in fucking lame. Sometimes when you click your heal spell she sits there in a stupor. When this happens you have to MOVE from that position and re-heal. Yeah I know, it's lame. But get used to it! When you have the Heal spell up only ally demigods, minions and yourself highlight. Ally demigods highlight GREEN and you highlight LIGHT BLUE. This is nice if you are behind a structure and can't see yourself very good you can still target yourself pretty easily. Also, when I am in healer mode I sit in the back and click my heal hotkey to bring it up and constantly scan over ally demigods to check their health. I cancel and re-click the spell every 5 seconds or so to avoid the cursor to time out on me.
Silence, if you look closely, cast in the same range as her little wind aura that blows around her. So if you are paying attention you can see if they are in silence range without hovering over the spell. Silence is an auto AoE cast and doesn't last very long. I try to use this to a) prevent heals or teleports, b] prevent being interrupted on a heal and c) when she has items to charge in and silence as many people as possible to start a fight.
Remeber her heal is fucked! Sometimes for no apparent reason when you cast heal and click on someone she will sit there and do nothing so you have to MOVE HER FROM THAT SPOT and cast heal again. This was annoying to begin with but I got used to it and I usually right-click spam movement until I see the heal cast.
I'll update when I think of new shit I forgot to mention.
Lemme know if you have any questions