Moving this build here off DDO forums. Seems a better spot and community.

Repeater on hit order as above puts imbue after weapon effects.
This is a completely untested idea. So it may work. Or it may not.
So mortal fear. Some people love it, some hate it. Personally, I think it leaves a lot to be desired. First, it only instant kills mobs if they are helpless and you are running combat brute or a lot of helpless damage. Second, it isn't available at level 20 when we first start doing EE content. And last it won't work in legendary content. So I figured why not make a build that "fixes" it to instant kill without helpless, starting at level 7, and also instant kills from level 7 through legendary content. Hence Mortal Fear 2.0. New and improved. As a side bonus, by the time you reach 30 and legendary content is released it should have DC's legends are made of. Of course, it also has solid spell power for on-hit AA imbue damage for bosses and healing/buffing. Plus trapping.
Plus since our instant kill is a vorpal weapon effect and not a spell or SLA, I think we get to totally bypass all spell resistance and epic resilience, which gives EE mobs +6 all spell saves while at full health. Maybe. I'm going to add this +6 save bypass into the DC as a bonus so you can compare it to a standard Necro.
Any Elf
1 Arti 1 Warlock 18 bard
Feats:
1 PBS Free: Repeaters / Rapid Reload / Trap finding
3 Precise Shot
6 Rapid Shot (Dex 13, tomes +1)
9 SF: Enchant 1 DC
12 ISF:Enchant 1 DC
15 PL:Bard or Wiz 1 DC
18 IPS (Dex 19, tomes +4)
20 Free: Warlock Pact
Stats:
Dex for Feats
Max Wisdom, all level ups in wisdom
Enhancements:
AA 27 4 DC 2 Wisdom
Elf 17 1 DC
SS Bard 34 8 DC
SE 2 4 Fort Debuff
Wisdom@20 = 18 + 5 level ups +5 tome + 2 ship + 7 item + 3 insight/quality + 8 ED + 2 Enhancement = 50
ED: Exalted Angel 3 DC
Twists: Wisdomx2, Draconic Presence and Spell School Specialist: Enchantment 6 DC
EE Spell Equivalent Level 20 terror arrows breakdown:
Vorpal and Not a Spell 6 DC
Feats 3 DC
ED total 9 DC
Item (Sage's) 3 DC
Augment and Ship Buff 2 DC
Enhancements 13 DC
Stats 20 DC
Base 20 DC
Cursespewing Endless Night Cannith Weapon -6 All Saves
Debuff Fort -4 Fort Save
Debuff Fear -2 All Saves
Puncturing Cannith Weapon (approx) -2 Fort Save
84 Terror Arrows DC, with -6 Fort applied on hit @ level 20. No consumables used. So DC 84 Will and DC 90 Fort save at level 20.
Spell Pen: Unnecessary: applied on-hit.