Phenomenal cosmic power! Itty-bitty birdie.

Quote Originally Posted by O'ren Ishi
O’ren Ishi, The Huntress

Spoiler: stub, etc
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Chaotic Anything Sparrow Hengeyokai Warlock 6 (OA and Dragon 318) Humanoid (Shapechanger)
-2 WIS, +2 DEX (hybrid)
Human Form: Medium, speed 30
Hybrid Form: Medium, Speed 20/fly 20, lowlight, speak w/ birds
Animal Form: Fine size (+8 to AC and to hit), lowlight, speak w/ other birds, Speed 1/Fly 50, AC 24 (+8 size, +6 Dex) STR 3, DEX 23, CON 10

Point Buy:
Str 10 Dex 10 Con 10 Int 16 Wis 15 Cha 15
Racial Humanoid / Hybrid
Str 10 Dex 10/12 Con 10 Int 16 Wis 13 Cha 15
+1 Cha at lvl 4

Least: Entropic Warding, 20% miss chance for ranged
See the Unseen: see invis and Darkvision

Least Blast Shape: Eldritch Spear: EB range is 250ft

Eldritch Essence Lesser Invocation: Baneful Blast (CM 123) choose a favored enemy from the ranger list, add +2d6 to EB damage, chain this w/ Favored Enemy Arcanist

Spoiler: build
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Level Class Base Attack Bonus Fort Save Ref Save Will Save Skills Feats Class Features
1st Warlock +0 +0 +0 +2 Conc 4, UMD 4, cc-Hide 2, cc-Move Silent 2, cc-Spot 2 Surrogate Spellcasting EB 1d6, Least Invocation (Eldritch Spear)
2nd Warlock 2 +1 +0 +0 +3 Conc 5, UMD 5, cc-hide/move/spot 2.5 - Detect Magic, Least Invocation (Entropic Warding)
3rd Warlock 3 +2 +1 +1 +3 Conc 6, UMD 6, cc-hide/move/spot 3 Flyby Attack DR 1/cold iron, EB 2d6
4th Warlock 4 +3 +1 +1 +4 Conc 7, UMD 7, cc-hide/move/spot 3.5 - Least Invocation (See the Unseen)
5th Warlock 5 +3 +1 +1 +4 Conc 8, UMD 8, Know Arc 1 cc-hide/spot 4 - EB 3d6
6th Warlock 6 +4 +2 +2 +5 Conc 9, UMD 9, Know Arc 3, cc-move 4 Born Flyer Lesser Invocation (Baneful Blast), Arcane Hunter ACF
Epic Feats:
Mortalbane x10, totals 50 uses/day of +2d6 damage to every EB

Spoiler: ACF Chain
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Baneful Blast gives you bonus damage to a selected Favored Enemy from the ranger list, thus giving you the ranger class ability minus the other useless bonuses. Selecting then the Arcane Hunter ACF to instead gain arcanists (anyone capable of casting arcane spells, or invocations) then allows you to add +2d6 damage to eldritch blast to any arcanist.
Eldritch/Baneful Blast
At 6th level and beyond in sparrow form, your to hit is +4 (BAB) +8 (size), +6 (DEX) = +18 vs a touch AC of usually 10. (It’s +14 at level 1.) Doing 3d6 base damage, +2d6 bane, +2d6 mortalbane. Even ignoring Precise shot, you still have a +14 to hit on your ranged touch, meaning auto success barring a roll of a 1 the entire build.

Spoiler: etc, etc
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A lesser chasuble of fell power (comp arc 148) is attainable in e6, which would add another 1d6 to your EB’s, for a total of 8d6 vs the right target. Gloves of Eldritch Admixture (MiC) may or may not be available in e6, but it’s also only up to 3x day, which is not awesome.

Optional Feats that require some arguing were you to take them:
Plunging Shot is an option for extra damage, as you’ll always be a speck in the air, and therefor always attacking from at least the requisite 30’ away, but the feat references a projectile weapon, and so would require your DM getting on board w/ EB being classified that way, which isn’t RAW, so isn’t included here.

Extra Invocation would grant another least invocation. The only thing worth it on this build might be summon swarm, which you could then argue would benefit from mortalbane, however it’s a close range invocation, which negates your greatest strength of being so far away, plus its duration is concentration, meaning it eats up all your standard actions, so meh.

Nemesis (BoED) is another good option for the warlock, which you can chain into Arcane hunter, however the text says “+1d6 to weapon attacks”. EB is a weaponlike SLA, but not a weapon attack itself, so this too would require some more DM hand waving, but would then bump you up to 9d6 on your EB vs evil arcanists. If allowed, dumping one Mortalbane just makes sense.

It’s hard to be original in a warlock round for e6, although I’m sure some others may do just that. Taking a Ranger ACF is about as original as I could think considering we all have the same invocations to pick from. Hengeyokai gives you flight, which otherwise would almost have to be your 1 lesser invocation.

Spoiler: SOURCES
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Book of Vile Darkness: Mortalbane
Complete Arcane: Warlock, Invocations
Complete Mage: Baneful Blast, Arcane Hunter
Monster Manual: Flyby Attack
Oriental Adventures/Dragon #318: Sparrow Hengeyokai
Races of the Wild: Born Flyer
Savage Species: Surrogate Spellcasting