Editing Warhammer 40,000/9th Edition Tactics/Space Marines (section)

===On Primaris Marines===
As these are the primary new toys given to Space Marines, a bit of caution should be taken when using them, especially when considering making an [[Ultima Founding]] Chapter, or using [[Crimson Fists|chapters]] [[Scythes of the Emperor|who]] [[Black Consuls|have]] been heavily supplemented by these new Chadmarines. The first and absolutely most important thing is that these guys are specialized to an extent that is jarring in comparison to other units in the codex. Almost every <s>Aspect Warrior</s> Primaris unit is a one trick pony, being very good at one role and struggling to do anything else: 
*For the most part, the characters take their roles deathly seriously, having no options that deviate from their purpose (if they even ''get'' options, that is- many of them don't even have that). They also have far fewer ways of accessing a 2+ save, so they have to be more careful around weapons whose AP is -2 or better. On the other hand, their profiles are a flat upgrade over an identically equipped normal character and they can be very nasty in close combat. 
*Aggressors are short-ranged shooting DISTRACTION CARNIFEXES that particularly rip apart light to medium infantry from short to mid-range and hit hard in melee, but their guns have to rely on the sheer quantity of the shots they put out against anything with a Toughness score greater than 5 and are sluggish enough to be at risk of getting blasted away before they get into the 18" range that most of their weaponry uses.
*Reivers are ranged or melee harassers with a powerful grenade capable of disrupting enemy units, some powerful deployment methods, and the potential to cause the worst problems for morale, but fare poorly against anything with morale boosts (or morale immunity, either inherently or due to small unit sizes) or armour saves above a 5+.
*Inceptors rely on their ability to deep strike and gun down their preferred prey (light infantry for Assault Bolters, everything else for Plasma Exterminators) but also suffer from range issues on top of poor melee ability, Suppressors combine the Inceptor's mobility with a long-range weapon whose secondary ability is ideal for softening up a unit you want to charge, but their autocannons aren't so hot against vehicles and they have subpar melee as well. 
*Infiltrators and Incursors are expensive and not that good against heavily armoured foes, but they are superb for quickly taking and holding objectives. Both can infiltrated and use smoke grenades to be hard to hit. The Infiltrators can bring in a mini-apothecary or count as being in range of a Phobos Captain/Lt.'s aura even if the Captain providing it is on the opposite side of the board, all while having a decent chance to wound even high-toughness units. The Incursors, on the other hand, are slightly better in melee, ignore cover with their guns, and ignore debuffs to hit in the shooting phase while also providing a source of mortal wounds from their haywire mines. 
*Eliminators can serve one of two functions. They can either pick off high-value infantry and characters even without a clear line of sight, or they can blast vehicles from afar with what's basically a shorter-ranged but more reliable lascannon. Either way, they can infiltrated to move into optimal positions and are a bitch to hurt with shooting when in cover. While they too are weak in melee the sergeant's optional instigator bolt carbine can act as a panic button if they're ever charged. 
*Eradicators are essentially Fire Dragons with a Primaris's stats. You might not have a Wave Serpent to get them deployed cheaply, but they're much more likely to survive footslogging anyway. With the extra shot they get from focusing on one target, they're most effective against lone vehicles and superheavies. 
*Outriders and Invader ATVs are your Bikers and Assault Bikes. Use them in the same way you would use their Firstborn equivalents, though kitting them out for melee might be wise given that Primaris have no other fast choppy units.
*Hellblasters and Intercessors are the exceptions that prove the rule, with the former acting as a solid MEQ/TEQ-killer that can also double as improvised anti-vehicle if needed and the latter being a more expensive but resilient Troops choice that's great at holding down backfield objectives. The two new Intercessor variants give them added roles as your main melee unit and a source of long range anti-infantry firepower which doubles as a counter to light vehicles, respectively. 
*Bladeguard Veterans are the closest thing you have to Assault Terminators. On the one hand, without Thunder Hammers they aren't as effective against anything tougher than a MEQ and their invuln is only a 4++, but on the other hand they have a 2+ armor save (unlike the majority of Primaris infantry) and can still shoot things. It also helps that they don't have the reduced mobility of a (non-Tartaros) Terminator and work well with an Impulsor transport. 
*Though the Repulsor does somewhat open them up to versatility, it pays significantly for multi-tasking and is often best for clearing out hordes; the Repulsor Executioner is its vehicle-killing cousin that shares the double-shooting trick of the IG's Leman Russ tanks. The Impulsor, on the other hand, has less transport capacity and can't carry Gravis-armoured units like Aggressors, but it's much cheaper and can be equipped for either greater resilience or for extra firepower. The Assault Vehicle option also opens up potential for some techniques that don't work with other transports. 
*The Gladiator is your answer to the Predator, with three different modes to use depending on what you need it to do: generalist/long range anti-vehicle, short range anti-vehicle, and anti-infantry. Same goes for the Storm Speeder, which also fills your anti-aircraft role in its Thunderstrike configuration. 

These guys are truly Aspect Marines and should be treated as such, even in a full army of the true scaled bastards.