Here the start of a 1000 point army.
The following three units go together as the death star unit for the army:
Death Star Unit
HQ: Commander Dante
Troops: Sanguinary Priest with Power Weapon
Elite: Sanguinary Guard with Infernus Pistol and Chapter Banner
Total of 555 points. Now, how to spend the remaining 445 points?
Option One:
Sanguinary Guard with Infernus Pistol
Tactical Squad of 5 Marines with Melta-Gun
Devastator Squad with 4 Missile Launchers
This list gives a second sanguinary guard as troops and a devastator squad for some heavy support. However, it leaves me with 100 or so points, which is hard to fill anything exciting. The extra troop will help to hold an objective in objective games I guess.
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Option Two:
Landspeeder with Multi-Melta and Heavy Flamer
Landspeeder with Multi-Melta and Heavy Flamer
Devastator Squad with 3 Missile Launchers
Tactical Squad of 5 marines with Melta-Gun and Razorback with Twin-Linked Lascannons
This list gives some fast moving attack options and snuggles the 5 man tactical squad inside a vehicle. the Razorback can provide some long range support. This is intended as an anti-tank/vehicle list.
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Option Three:
Devastator Squad with 4 Missile Launchers
Landspeeder with Typhon missile launchers
Assault squad with ten marines, thunder hammer and flamer
It has a strong assault squad (but could be a little stronger) and reasonable long range support.
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Option Four:
Devastator Squad with 4 Missile Launchers
Devastator Squad with 4 Missile Launchers
Tactical Squad with five marines and Razorback with twin-linked lascannons.
Missile spam!
In this option could substitute the tactical squad and Razorback for an Assault Squad with 7 members, thunder hammer and a flamer/meltagun.
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These last two options will require the minimum purchase of new models :)
Option Five-I
Devastator squad with 4 Missile Launchers
Tactical Squad with 10 marines, flamer, Missile Launcher, and power fist and Rhino
Landspeeder with Multi-Melta and Heavy Flamer
Option Five-II
Devastator squad with 4 Missile Launchers
Tactical Squad with 10 marines, flamer, Lascannon, and power fist
Baal Predator with flamestorm cannon