This is my current Sedna build.  It sacrafices early pounce and demigod killing power for healing and HPS.  The build is designed to provide excellent support, hold flags and draw attacks and mana from the opponent. You will likely win games based on war score alone by denying flags.  As with any Sedna build, if you have bad teammates it won't matter what you do.  You will only be a serious threat to other demigods after level 10.

Favor Item:  Blood of the Fallen

Skills:
Level 1:  Heal 1
Level 2:  Inner Grace 1
Level 3:  Healing Wind 1
Level 4:  Heal 2
Level 5:  Healing Wing 2
Level 6:  Inner Grace 2
Level 7:  Heal 3
Level 8:  Inner Grace 3
Level 9:  Counter Heal/Pounce 1 (depending on whether the opponent has Priests out)
Level 10: Heal 4
Level 11:  Pounce 1  (assuming you took Counter Heal at 9(
Level 12:  Pounce 2
Level 13:  Pounce 3
Level 14:  Pounce 4
Level 15-20  Magnificent Presence, Silence or Life's Child as suits you, but the game should be over by now anyhow.

Equipment

Start:  Monk Idol
1750:  Vlemish
1800:  Currency 1
2100:  Nimroth + Scale Mail
1500:  Unbreakable Boots
4000:  Narmoth's Ring
4000:  Sell Banded, buy Grofling

Depending on your war score and the situation, buy pots, scrolls and locks as needed

Strategy:
Early game (Pre-Vlemish).  You have enough mana for two heals.  You will want to fight head-to-head for flags, knowing that nobody else has a whole lot of mana.  Soak up attacks and then heal, which will usually force your opponent to retreat.  Try to hold off on your heal as long as possible in order to keep your opponent in the fight.  Maintain your flags and farm creeps.  Avoid all double teams.  Use your monks to keep you in your fights longer, but keep them behind you.  This takes some management.  If you are in your lane alone, order your monks to stand by the flag and attack the tower solo.  Retreat to your monks for healing when still above 50%.  Wash, rinse, repeat.

Early game (Post-Vlemish):  Getting currency as quickly as possible will make things easier later in the game for buying creeps and better armor.  You will have a bit of speed now, thanks to Inner Grace and you will be able to run past the first towers without much problem.  Keep an eye for anyone looking squishy or slow.  They will often retreat to their tower assuming you will break off.  You can now pursue past towers which can net some kills on the unaware.  Be extremely careful, though, because you still do not have armor.  An enemy DG coming in behind you while pursuing, teleporting in, or a sniper anywhere on the map will ruin your day.  Keep your monks on the field healing your teammates when you return to upgrade.  There's no point in having them with you at the shop.

Mid game (Pre-ring):  You now have good armor, health and very high HPS.  You can also heal 1200 health.  You're now a hard kill.  Your damage is still low.  You still will want to dominate flags and lanes.  Concentrate on pushing back enemy DGs or forcing them to spam their mana on you.  As you become more confrontational, your biggest threat is a stun.  Although it happens rarely, getting stunned out of a heal is usually a death sentence.  Concentrate on the meta-game and protecting your teammates.  Grinding down towers is a priority now.

Mid game (Post-ring):  At this point, you're a formidable tank.  You should have near to 6,000 HP and the addition of Narmoth's ring will give you healing on hit.  You should be able to pursue past more than one layer of towers with ease.  Anyone slower than you is a target.  Pounce is now added to your arsenal.  You can use pounce for one of three things:  First, it's usually good to open an attack with it.  Most opponents will open with a skill (venom, mines, etc) and the opening pounce will often catch them.  Second, if they do a big wind up move, use pounce.  This will stop hammer slams (when there's no boulder roll before), teleports, heals, and so on.  Third, use it as a finishing move.  When pursuing, watch their HP to drop below your pounce damage and then pounce them. Do NOT pounce whenever it is available.  You will run out of mana.

Late game:  You're almost impossible to kill at this point.  You're healing over 100 HPS, you have great armor and stacked health.  You will go from no pounce to a 1000 damage pounce in 4 levels.  Opponents who were used to slugging it out with you will now find you're much more dangerous.  They will tend to flee too late, and then get caught by your pounce.  Tower damage is trivial and you can sail into their backfield capping flags and portals or finishing off kills.  You should have a War Score lead and cap-locking their portals will end things quickly.

What has changed from the first Panther build? 
1.  Added monks as starting purchase
2.  Removed Slayer Wraps
3.  Switched order of Inner Grace 2 and Healing Wind 2
4.  Added Narmoth's ring
5.  Removed Platemail

Why take monks?  You hate monks!  True, I hated them because they never healed when I wanted or needed them.  And monks are still not good in an aggressive build.  I've changed my build to even less aggressive than before.  An aggressive monk-free Sedna is good when you have great teammates, but in pub games, I found I would be punished for being aggressive too often due to lack of support.  Using monks early opens up some new strategies.  First you can take on towers immediately when you're alone.  You will not need pots or heal (i.e. mana) to get back to strength, which means you can retreat to the flag you're holding and wait for your monks to heal you back up.  Second, they help in getting you money because their added damage makes farming easier.  Third, they support your teammates.  You can leave them on the battlefield whenever you need to go into town.  I never upgrade from monks.  By level 8 to 10, most levels of priests will die very easily.  Relying on them in a battle is dangerous.  Therefore, I really only count on them for healing out of combat.  In those cases, monks will heal just as fine as bishops.

Pathing still sucks.

Why not take pounce earlier?  Simple:  mana.  Pounce does less damage per mana than heal recovers health.  The build focuses on always having heal available.  You do not have the DPS to seriously threaten many DGs unless you've been locked in melee for some time.  So you don't really have much chance to get DG kills at low level anyhow.  The benefits of skipping pounce are better healing and faster speed, both which will keep you alive at lower levels.

What about silence?  Silence has a short duration and takes a ton of mana.  Builds centered around silence require much more mana than this one.  This build is sacraficing mana for health and HPS.  The typical silence use would be combined with pounce or supporting a gank.  While these are legit strategies, they're not used in this build.  Hey, you can't do everything.

How will I die? And how do I prevent it?  You'll likely die for the following reasons:
1.  You were stupid.  You got your health and armor up and decided you were invincible.  You ran after that Reg with 1,000 health left and find yourself surrounded in the middle of the enemy's towers.  Solution:  Don't be stupid.  Play zoomed out enough to see what's going on in other lanes and retreat early and often.
2.  Your teammates were stupid.  Your teammate is fighting and you and an opponent rush to help.  You throw down your heal on him (or her) and they run away anyhow.  You're then stun-ganked while waiting for your heal to cool down.  You bait two 1/3 HP enemies into one of your fresh teammates.  Your teammate farms creeps instead of helping you out.  Etc.  The ways to die from stupid teammates is almost infinite.  Because you are always risking your own safety by healing teammates and you rely on them for higher DPS attacks, Sedna will always have this weakness.  If you can't handle this, I suggest UB, Reg, TB or tower Rook.
3.  You were stun/slow-ganked.  There are some nasty combos out there that will kill you before you can heal.  UB foul grasp - Ere swarms across you - Ere charms/bites is particularly nasty.  Reg Shrapnel mines - TB fireball - Reg snipe.  Posion dagger while you're in a Rook tower farm.  Solution:  Rember that level 3 heal clears all status effects.  This will wipe out slow effects including poison dagger.  Heal them off even if you're at full health.  Most of these situations can be avoided by remaining aware.  But remember you are a target, especially early on.  The enemy will not be afraid of your DPS but will want to remove your heals.