Looks pretty cool! I like the cryptic personality - fits arcane very well. It is the art of secret knowledge, is it not?
For Sarenax, here's an outline of what I was thinking for his background.
Upon his birth, his black scales marked him as different from the rest of his small tribe. They were superstitious, pronounced him a 'curse', and exiled him while he was still very young. Even though the tribal elders based the decision solely on his coloring, they were partially correct. Sarenax was chosen before his birth by the Raven Queen to become her agent, to bring the sweet embrace of oblivion upon some entity, though the identity of that entity is still unknown to Sarenax.
Over the course of his adult life Sarenax has learned to channel the Queen's power, becoming a deadly vessel of the final sleep and earning a reputation as such. When his black scythe appears in his hands whoever faces him knows their doom has been pronounced - death's agent has come. That is, if they see him coming.
Also, I have an experiment. You say that copying that summary into the CB should generate the right character. "Well, it's just a bunch of text," I say to myself. "I don't have the CB, but what if I copied my stuff over what stonegod posted?" So, here's the experiment: someone paste this into the CB and see if it gives you Sarenax
[sblock=Sarenax for the CB]====== Created Using Wizards of the Coast D&DI Character Builder ======
Sarenax the Reaper, level 21
Dragonborn, Cleric, Angelic Avenger, Harbinger of Doom
Build: Battle Cleric
FINAL ABILITY SCORES
Str 24, Con 13, Dex 16, Int 10, Wis 20, Cha 16.
STARTING ABILITY SCORES
Str 16, Con 11, Dex 14, Int 8, Wis 14, Cha 12.
AC: 37 Fort: 32 Reflex: 29 Will: 31
HP: 140 Surges: 10 Surge Value: 36
TRAINED SKILLS
Bluff +18, History +17, Insight +20, Religion +15, Stealth +21
UNTRAINED SKILLS
Acrobatics +13, Arcana +10, Athletics +17, Diplomacy +13, Dungeoneering +15, Endurance +11, Heal +15, Intimidate +15, Nature +15, Perception +15, Streetwise +13, Thievery +13
FEATS
Level 1: Toughness
Level 2: Armor Proficiency (Scale)
Level 4: Skill Training (Stealth)
Level 6: Durable
Level 8: Weapon Focus (Heavy Blade)
Level 10: Raven Queen's Blessing
Level 11: Lightning Reflexes (retrained to Opportune Reflexes at Level 21)
Level 12: Armor Specialization (Scale)
Level 14: Uncanny Dodge
Level 16: Skill Focus (Stealth)
Level 18: Restful Healing
Level 20: Secret Stride
Feat User Choice: Implement Expertise (Holy Symbol)
Feat User Choice: Weapon Expertise (Heavy Blade)
Level 21: Epic Resurgence
POWERS
Cleric at-will 1: Righteous Brand
Cleric at-will 1: Priest's Shield
Cleric daily 1: Avenging Flame
Cleric daily 15: Holy Spark (replaces Avenging Flame)
Cleric daily 19: Indomitable Spirit (replaces Rune of Peace)
Cleric daily 5: Rune of Peace
Cleric daily 9: Divine Power
Cleric encounter 1: Healing Strike
Cleric encounter 13: Inspiring Strike (replaces Healing Strike)
Cleric encounter 17: Blinding Light (replaces Split the Sky)
Cleric encounter 3: Split the Sky
Cleric encounter 7: Strengthen the Faithful
Cleric utility 10: Mass Cure Light Wounds
Cleric utility 16: Divine Armor
Cleric utility 2: Bless
Cleric utility 6: Bastion of Health
ITEMS
Cloak of Displacement +4, Imposter's Nagascale Armor +5, Gloves of Storing, Jagged Fullblade +5, Distance Javelin +3, Black Feather of the Raven Queen +3
====== Created Using Wizards of the Coast D&DI Character Builder ======[/sblock]