Okay, here is my version. It is not fully thought through yet but just finished. Allow me to make some remarks:
1. I did decrease some of the stats in order to avoid any chance of giving a Mary Sue impression and because I think the edge of the LOTD comes from its supernatural abilties. Otherwise they are not too different from normal Marines. Low Ag because if want them to be more of the slow kind, low Fel because their appearance isn't too likable.
2. No running, as per 40K
3. Shortened the profile and all-in-all minor changes to skills only, all of them debatable, nothing really important in my mind. Talents: again, I prefer them to not really be much better than regular Marines. Swift attack because of 40K A2. Combat Formation because of 40K I4. TWW they should have for bolt pistol/chainsword combo. Crack Shot/Crippling Strike for a nasty surprise should they ever critically hit someone.
4. Traits: I have tried to emulate the 40K Invul save by making them have a quasi-Force Field per their unique trait. Int+10/(100-WP) are the de facto Force Field ratings (unless it's a delayed attack striking in the right moment that the Legionnaire is not aware of or a psy attack). This is the part least thought through. It makes the LotD vulnerable to clever tactics though. Not entirely made up about this.
5. New ammo: it's based on the LOTD description in the Codex. Might be overpowered, alternatively ditch the entire Vengeance rounds part and just make them cause their victims to be on fire.
6. I ditched all the hatred talents. I see the LOTD more as collected, solemn fighters. If you want similar bonuses though, I'd rather recommend the Slayer of Daemons, etc line of talents.
7. Number of wounds is debatable, I have not thought it through fully.
In short - if a DW KT was to fight a LOTD (half-)squad, the DW's edge should be the high-tech gear, etc. The LOTD's edge should be it's supernatural abilties.
So without even further ado:
Damned Legionnaire (Elite)
S 55 (12)
T 50 (10)
(this layout makes for better reading here)
Movement: 4/8/-/-; Wounds: 30
Skills: Astartes Skills, modified in the following manner: add/replace with Forbidden Lore (Warp) (Int) +20, Intimidate (S) +20, Silent Move (Ag) +10, Tactics (Assault Doctrine) (Int) +20
Talents: Astartes Talents, modified in the following manner: add Combat Formation, Crack Shot, Crippling Strike, Swift Attack, Two-Weapon Wielder(Ballistic), Two-Weapon Wielder(Melee)
Traits: Astartes Implants, Auto-stabilised, Fear (2), From Beyond, Indomitable(new), Spectre from the Warp(new), The Stuff of Nightmares (special: holy attacks do no damage, daemonic attacks do wound), Unnatural Strength (x2), Unnatural Toughness (x2)
Weapons: Astartes Bolt Pistol (35m; S/2/—; 2d10+7 X; Pen 5; Clip 10; Rld Full; Tearing, Reliable), Frag Grenades (36m; S/-/-; 2d10+2 X; Blast (5)), Krak Grenades (36m; S/-/-; 3d10+6 X; Pen 6), Combat Knife (1d10+14 R; Pen 2) and one of the following:
• Astartes Bolter (100m; S/2/4; 2d10+7 X; Pen 5; Clip 28; Rld Full; Tearing, Reliable)
• Flamer (30m; S/-/-; 2d10+4 E; Pen 3; Clip 6; Rld 2Full; Flame)
• Plasma Gun (90m; S/2/-; 1d10+11 E; Pen 6; Clip 20; Rld 8Full; Overheats, or 100m; S/2/-; 2d10+11 E; Pen 8; Clip 20 (3x ammo use); Rld 8Full; Overheats, Recharge)
• Meltagun (30m; S/-/-; 2d10+10 E; Pen 13; Clip 5; Rld 2Full; +1d10 damage at Short Range)
• Heavy Bolter (120m; -/-/10; 2d10+12 X; Pen 6; Clip 60; Rld 2Full; Tearing)
• Heavy Flamer (30m; S/-/-; 2d10+8 E; Pen 6; Clip 10; Rld 2 Full; Flame)
• Lascannon (300m; S/-/-; 6d10+12 E; Pen 10; Clip 5; Rld 2Full)
• Missile Launcher with Frag (250m; S/-/-; 2d10+6 X; Blast (6); Clip 1; Rld Full) and Krak (250m; S/-/-; 4d10+10 X; Pen 12; Clip 1; Rld Full) Missiles.
• Multi-Melta (60m; S/-/-; 4d10+12 E; Pen 16; Clip 10; Rld 2Full; Blast (1); +1d10 at Short Range)
• Plasma Cannon (180m; S/-/-; 3d10+12 E; Pen 8; Clip 24; Rld 2Full; Overheats, Unreliable, Blast (1)) or (190m; S/-/-; 4d10+12 E; Pen 10; Clip 8; Rld 2Full; Overheats, Recharge, Unreliable, Blast (3)) on full power.
Armour: Astartes Power Armour (Body 10, Heady 8, Arms 8, Legs 8)
Indomitable(new): The Legionnaire cannot be possessed, mind-controlled or otherwise mind-influenced through warp-based powers, including the reading of thoughts.
Spectre from the Warp(new): The Legion of the Damned marines are travellers between the Warp the real world.
• Normally they exist only in the Warp Form where they can be detected with Psyniscience. Transitioning into the real world or back costs a Free Action and takes 1 full turn during which the Legionnaire has the Incorporeal Trait.
• In the Manifest Form the Legionnaire is a semi-corporeal being. He flickers between physical and incorporeal state and only due to an act of will he can persist as a real world entity. When it is the Legionnaire's turn and he is in Manifest Form he can act as if a normal Marine in the flesh. He can also evade attacks against him that he is aware of by phasing out at a blink of an eye by spending his Reaction and succeeding an Intelligence+10 test. If he succeeds, he counts against that attack as Incorporeal. When it is not the Legionnaire's turn, he can be assumed to be flickering. For every attack that hits, the Legionnaire must make a Willpower+0 test. If he fails(!) it, the Legionnaire has shifted out of the physical realm and counts as Incorporeal against the attack.
Warp Bolts(new): The Legionnaire's bolt weapons shoot ammunition that is not from this world. In game terms they count as Vengeance rounds without a chance for malfunction. For each attack that hits, the victim must pass an Agility test or be put on fire.
So, please let me know what you think of it.