Rilla-Sneasler is a fantastic offensive core, can attest to using it myself on a lot of my builds even pre-DLC, would like to submit a great mon that I think can be easily tacked onto this:
Rilla-Sneasler-Zamazenta
Rillaboom @ Choice Band
Ability: Grassy Surge
Tera Type: Grass
EVs: 128 HP / 252 Atk / 4 SpD / 124 Spe
Adamant Nature
- Grassy Glide
- Wood Hammer
- Knock Off
- U-turn
Sneasler @ Grassy Seed
Ability: Unburden
Tera Type: Dark / Ghost
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Dire Claw / Gunk Shot
- Close Combat
- Lash Out / Shadow Claw
- Swords Dance
Zamazenta @ Leftovers
Ability: Dauntless Shield
Tera Type: Steel
EVs: 44 HP / 252 Def / 40 SpD / 172 Spe
Jolly Nature
- Body Press
- Heavy Slam / Stone Edge
- Crunch
- Iron Defense
More traditional Max-Max/Sample EV spreads can be run, these are just my personal spreads (Rilla outspeeds min speed Zap and the rest in bulk, Zama has a significantly stronger press than the sample set and maximises lefties + terrain % healed at the expense of some special bulk).
These mons all break for one another and provide fantastic offensive synergy, I got reqs for the
Gambit,
Bloodmoon and
Roaring Moon suspect with builds all using this core and used it in
one of July's featured RMTs. All 3 apply heavy pressure to Flying types like Zapdos and Moltres that are tasked with switching in on Fighting attacks and Wood Hammer, and possibly the #1 hard stop to Sneasler and Zamazenta is Dondozo; Rillaboom is one of the very few physical attackers that can OHKO Dozo with its banded Hammer while Tera Grass Hammer even has a 75% chance to OHKO a max Phys.Def Gliscor from full.
Move Choices:

Drain Punch can be used on Rillaboom to hit Kingambit, but this core has Zamazenta to deal with Gambit, while Sneasler OHKOs and resists Sucker Punch, so Knock Off to remove Heavy-Duty Boots from Flying types and deal huge damage to Gholdengo and Slowking-Galar is preferred. High Horsepower is a niche option to hit Heatran while also hitting Ghold and Gking, but Knock Off is usually better and forces progress against the opposing team.

Although Acrobatics is a strong option on Sneasler, I find that this core does not struggle with Great Tusk and a move to hit Slowking-Galar, Gholdengo and Dragapult, mons that can be a significant roadblock to Zamazenta in particular, is much more valuable. Lash Out is my preferred option, maintaining your resistance to Kingambit's Sucker Punch even post-Tera, while Shadow Claw hits the same targets and gives you an immunity to Dragonite's Extreme Speed at the expense of a weakness to Sucker. Sneasler also has the option to run Gunk Shot as a non-contact option that OHKOs Zapdos at +2, but I personally enjoy the consistency of and chance to get bailed by Dire Claw.

Stone Edge is an option on Zama to act as a lure to either KO or significantly damage Zapdos and Moltres, paving the way for Rillaboom and Sneasler to be a problem for the enemy team. However, I personally prefer Tera Steel Heavy Slam for the OHKO on Valiant and Enamorus and the 2HKO on Clefable.
General Set Choices:

Choice Banded Rilla is a fantastic breaker able to muscle through the main Phys.Def Unaware mon in the tier in Dondozo, while also enabling Unburden on Sneasler and providing Zamazenta with extra passive recovery that it greatly appreciates. Knock Off is very effective too with Stealth Rock support, as Flying types that load well into this core do not appreciate having to take heavy hazard chip.

Grassy Seed SD Sneasler pairs excellently with Rillaboom, able to activate its Unburden on demand and deal heavy damage or eliminate key targets that are also tasked with checking Rilla like Zapdos and Moltres. Often, Sneasler will not even need to set up an SD before it accomplishes its task of breaking those targets, but it can also be preserved as an endgame cleaner into a team weakened by the other members of this core.

Leftovers with Iron Defence allows Zama to function as a potent wincon that can sweep through teams with weakened Ghost, Psychic and Flying types, which makes it a fantastic pairing with Dark/Ghost coverage Sneasler in particular. Terrain support lets this mon 1v1 almost any physical attacker in the tier, and Tera Steel resists Moonblast and grants a crucial immunity to Gliscor's Toxic, letting you set up Iron Defences on it and take almost nothing from EQ especially with terrain up.
Threats:

Gliscor hard walls Sneasler, takes very little from any of Zama's attacks and while Rilla can almost guaranteed OHKO it with Tera'd Hammer, unless you are playing against stall where Rilla has a fantastic matchup with Tera Grass you may often want to save Tera for one of your other mons on the team. Zamazenta can set up on Gliscor and beat it 1v1 with Tera, but this is again reliant on you having that to play around Toxic; Slam-less Zama with Substitute feels almost unusable in the current meta with Val and Clef. Good teammates that can deal with this mon include Hatterene, who can also make use of Terrain to run Grassy Seed or simply get more passive recovery, and your own Gliscor, who can use this mirror matchup as an opportunity to get up your own entry hazards.

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Both of these mons wall all 3, with Moltres in particular being a threat due to Flame Body. However, with offensive pressure you can often break through them and allow for another member of the core to sweep; I've often sacrificed Sneasler for a large amount of chip on Zapdos so that later it cannot take a Grassy Glide from Rillaboom, or I only have to risk one Static proc while attacking with my Zama. I have previously used Gliscor and Ting-Lu to answer the two and use them to get up hazards, but a more offensive build can even forego this for more mons which pressure and can remove these defensive Flying types.

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Amoonguss can tank most of this core's attacks, and a mon that can take advantage of it like Heatran is often a good pick with Grassy Terrain. If you do let it Spore one of your other mons though, Sneasler and Tera Steel Zama can use it as setup fodder, with the latter notably blocking Clear Smog and taking very little from Foul Play. Pex is a similar story, able to force out Sneasler and Haze both it and Zamazenta, but Wood Hammer deals massive damage and Sneasler will often drain enough Recovers with its ability to hax with Dire Claw to leave Pex unable to handle the rest of the team.

While Dondozo drops to Wood Hammer, if they Tera into a Grass resist they wall all 3 mons, and even without Tera it's not a good feeling to have it force out your Sneasler and burn your Unburden. Mons that can force progress with Knock Off like Great Tusk, Samurott-H and Roaring Moon are good picks for teams with hazards that are able to pressure it with that, while strong special attackers like Iron Valiant and Dragapult that can force it out are also valuable teammates.

Speed Booster Moth is one of very few offensive mons that this core cannot out-offence, as Sneasler, even when outspeeding it, cannot KO it and in return is OHKOd by Psychic variants or takes massive damage from Fiery Dance, while Rillaboom cannot touch it with Grassy Glide. Zamazenta lives any hit from full, but needs +6 to kill it with Body Press, although +4 is enough after rocks. Heatran, Sp.Def Gliscor and Ting-Lu are again good picks defensively into Moth, while other noteworthy options include Empoleon and Garganacl.

Opposing ID Zama can take advantage of your own Grassy Terrain to set up, on paper able to 1v1 all three members of this build after a single ID. Knock Off from Rillaboom can severely limit this, and they are unable to switch in hard on Hammer, while Sneasler can often fish for hax as they need several IDs to KO with press and I run 172 Spe Zama specifically to outrun and 1v1 the sample Zamazenta spread. Mons that can handle Zama even if it sets up like Cresselia, Gholdengo and Dragapult are useful picks to help with this matchup, and Gliscor can assist here too if they aren't Tera Steel or Poison.
Notes:
Other good teammates that I've found useful for this core are Cinderace, Great Tusk and Kingambit, with all three appreciating the chip healing of terrain while providing utility in hazard removal in the case of the first two, and alternative sweepers in the latter two. This build also invites a lot of Fairy and Flying type attacks, and so a solid Steel type or alternative resist is appreciated so as not to be too reliant on Tera Steel Zama. Many mons that lack reliable recovery like Manaphy, Volcanion and Heatran enjoy making a home on Terrain teams, and for a HO build with this core alternative support in Aurora Veil from Ninetales-A or even Sticky Web from Ribombee can be considered. Lastly, powerful breakers with poor longevity can be considered as more niche picks; Guts Ursaluna appreciates being able to maintain and actually leverage its bulk, and even Life Orb attackers like Greninja are able to get more turns from the gradual healing of terrain.
Rilla-Sneasler is definitely the more common element of this core, with those two in particular being the overall highest-usage combo of two mons in SCL
as of Week 4. However, despite its much lower usage in tandem with these two, I think that Zamazenta is at least worth consideration as a third pick to support and complement the pair, and the underutilisation of this is more due to a reluctance to build around mons with shared weaknesses when those can instead be turned into shared checks.