The last two Elites choices are a bit mismatched, being the only ones without multiple versions in the slot. Even so, discussing them will bring some 40K back into they Warmahordes dominated week here in the Fourth Company Librarium.
Legion of the Damned
The Legion of the Damned took a cut in points cost and went from being a laughable unit to a very effective but niche unit. Legionnaires have the statline of veteran Space Marines with LD10. The also have Fear and Fearless, as well as Slow and Purposeful. All of their weapons Ignore Cover and their power armor save is invulnerable. All in all, a tough package for a few more points than Sternguard Veterans. Legion squads always have to arrive by Deep Strike, but they get to re-roll the scatter dice when they arrive.
Combined, these rules make Legion of the Damned an excellent unit to Deep Strike into the enemy army and light up an important enemy unit. Their reliable placement, ability to fire heavy weapons when they arrive, and Ignore Cover allow them to do more damage on the drop than any other Space Marine unit. Most commonly, Legionnaires are armed with a meltagun, combi-melta, and multi-melta in order to destroy an enemy heavy vehicle. They even reliably kill skimmers as they ignore Jink saves. However, they can be armed with plasma weapons to kill heavy infantry or flamers (including a heavy flamer) to wipe out light infantry.
I’ve heard some players like to put a combat weapon on the Sergeant to take advantage of his WS5 and 3++. He will do well in challenges, but this isn’t necessary. Legion of the Damned squads will likely destroy their target on the drop before being gunned or cut down the next turn. Even so, the Legionnaire Sergeant looks pretty awesome with a power fist or axe and he makes better use of the weapon than most Sergeants, so take it if you like the look.
Centurion Assault Squad
Assault Centurions are a new unit, designed to be an alternative to Assault Terminators. Wearing Centurion armor, they boast S5, T5, two wounds, and a 2+ save but no invulnerable save, along with Move through Cover, Slow and Purposeful, and the ability to fire two weapons. While they only have one attack on their profile, they have paired siege drills, giving them two S9 AP2 Armorbane attacks. Most importantly, these attacks are made at normal initiative. They come with ironclad assault launchers, which they can replace with hurricane bolters, and a twin-linked flamer, which they can replace with a twin-linked meltagun. They can also take an omniscope, which allows the Sergeant to split fire. This is particularly useful if you take the entire squad with meltaguns.
Assault Centurions cost more than Assault Terminators, and are more durable in exchange for having fewer attacks for the points. Between their siege drills and meltaguns, Assault Centurions are amazing at destroying vehicles and buildings. They’re also pretty good at fighting hard targets. Their main downfall is a lack of mobility. With no ability to deep strike, they can only move into position to launch an assault using a Land Raider. As Very Bulky models, you’ll have to take a Crusader if you want to transport more than a minimum squad.
All in all, Assault Centurions aren’t a bad choice, though they are very specialized to killing vehicles and buildings. Without a good way to reach the enemy, they will only make it into assault if your enemy wants them to.