One of the big topics among 40K players right now seems to be how to use the newly returned Primarch, Roboute Guilliman, effectively on the tabletop. More specifically, most of these discussions seem to center around how to keep him alive efficiently, since he is a Monstrous Creature and thus cannot join units, ride in transports, or even embark inside fortifications.
While the Victrix Guard formation exists and has special rules that allows Guilliman to use Look out Sir! with its members, it is an inherently expensive formation and perhaps not the most efficient way to keep him alive against powerful enemy shooting, especially the ever-prevalent Graviton weapons in the current meta.
As I have thought about, I think one of the best body guard “battle groups” for Guilliman might look something like this:
-3-5 Bullgryns (with Carapace Armor and Slabshields)
-Sevrin Loth (selecting the Telepathy, Invisibility, Terrify, and Psychic Shriek powers)
The way this works is pretty simple: the Bullgryn squad (with Loth attached) “bubble wrap” Guilliman to obscure him from enemy shooting from all different directions. Because of their special Slabshields, they provide him with 4+ cover save, instead of the normal 5+ cover save provided by intervening models. Loth then casts The Shrouding, granting the Bullgryns a 3+ armor save/5+ cover save in the open and giving Guilliman a 2+ cover save (i.e. Bullgryn cover + Shrouded), which is a significant step up from his normal 3++ save against AP2/1 shooting attacks (like Grav and Plasma Weapons).
By itself, this would be a solid improvement in the Primarch’ survivability, but Loth has one more trick up his sleeve… Invisibility. If he can successfully cast this on Guilliman as well, then all enemy shooting is hitting on 6+, which drastically improves his durability, especially if successfully combined with a 2+ cover save from The Shrouding, as described above. With both of these powers successfully cast and the Bullgryns screening, it takes an average of 54 x BS4 Grav Cannon/Amp shots to cause a SINGLE unsaved wound on Guilliman (so 324 Grav Cannon/Amp shots to kill him outright).
An added benefit of this battle group is that the Bullgryns/Loth are a solid “anvil” unit in their own right and, aside from combining to give Guilliman enhanced protection, they can easily tie up (or even defeat) enemy “chaff” units, thus freeing the UM Primarch to use his assault abilities against the more important enemy forces, where his mass S10 AP2/S: D attacks can really make the biggest impact (Note: Loth can use his 2++ to tank low AP attacks for the Bullgryns and the Bullgryns can use their 3W per model and T5 to absorb high volume attacks away from Loth).
Now, there are some drawbacks to this battle group: first, while not as crazy as the Victrix Guard, it is still pretty points intensive for a normal 1750-2000 point game and also requires at least two CADs/Allied Detachments (i.e. one Astra Militarum for the Bullgryns, one Red Scorpion one for Sevrin Loth, with Guilliman taking up a LOW slot for either one of them). Additionally, it does require successfully casting two WC2 powers a turn to work at maximum efficiency, which is pretty hard to do reliably (even with a PML(3) caster like Loth). Finally, everyone (including Guilliman) is still on foot and so can only move up 6″ + D6″ run each turn, which means agile opponents can still avoid getting charged by these units (even if they have a very difficult time hurting them, especially Guilliman).
On the other hand, if these units do get into combat, they will wreck house, especially with the close combat prowess and buffs that the UM Primarch brings to the table, Perhaps equally important, this battle group has the capacity to absorb TONS of firepower away from the rest of your army, which in turn can allow them to maneuver, shoot, charge, seize objectives, cast powers, etc. etc. with relative impunity… I think a mechanized Astra Militarum force or an elite infantry heavy Red Scorpion army in particular could do really well with this kind of support, especially since the types of weapons they are vulnerable to are exactly the weapons your opponent will have to divert to trying to kill Guilliman.
Overall, this is battle group is definitely not an “auto-win” choice, but if you are planning to field Guilliman anyway and have a strategy built around keeping him alive and getting him into close combat, then I think it can be an effective addition to your Imperium of Man task force.