Gonna stop lurking and pitch in for the first time on this Rillaboom conversation. As someone who has been using this grassy offense team peaking in the 1800s (removed EVs as to not fully give away the sets, still very much working with this core even with Moon banned) and have been regularly on the leaderboard since Gouging Fire suspect 1 and until the recent Roaring Moon ban. With this I can confidently say that the weakness of Rillaboom is far overblown. Though Rillaboom may struggle into certain meta prevalent Pokémon such as Zapdos, Moltres, Pecharunt and Kingambit, it is by no means awful.
The utility and support Rillaboom provides is unmatched. With Terrain Extender, it can provided consistent chip healing for a majority of games, allowing for mons who otherwise would run Leftovers to run other items, and providing a larger window of opportunity to for those who rely on Grassy Seed. Additionally, another added benefit of Terrain Extender is not locking Rillaboom into one move, this allows Rillaboom the ability to either use Knock Off to make progress or Wood Hammer to significant damage, and then U-Turn out. Moreover, certain Pokémon who are normally faster than Rillaboom get lulled into staying in believing Rilla to be locked in either Knock Off or Wood Hammer, meaning it can get a jump on them with Grassy Glide and collect a surprise KO. Grassy Terrain as a supportive tool is unmatched, and provides so much to any time.
Not only does it provided meaningful chip healing as mentioned prior, it also enables a many offensive tools. For example, Hawlucha greatly appreciates the presence of Grassy Terrain, as it provides it with +1 Def as well as activating Unburden. With this Hawlucha with proper investment can be suprisingly bulky, living moves it would not normally otherwise, such as Ice Shard from Weavile. Hawlucha also handles many of the threats which unbanded Rillaboom thuds into, such as Zama and Kingambit. In a similar vain, Raging Bolt is amazing with Grassy Seed and Grassy Terrain support. With proper investment and the +1 Def from Grassy Seed, with full HP Bolt is able to comfortably live Headlong Rush from Great Tusk, and revenge kill it. Grassy Seed provides enough bulk that it pushes Raging Bolt out of the threshold of many certain kills otherwise, and the residual healing gives Bolt surprising longevity. Lastly, arguably the biggest beneficiary of Rilla's Grassy Terrain is Ogerpon. The additional power provided to Ogerpon's Powerwhip is invaluable. Grassy Terrain makes getting certain kills significantly easier, allowing for unboosted whip to OHKO some standard Ting-Lu sets, 2HKO standard Dondozo, and provide more favoruable rolls on Stall and BO regulars such as Gliscor, Clefable and Clodsire. With the presence of Grassy Terrain, Ogrepon becomes a ludicrous wallbreaker, synergizing extremely well with Cornerstone, as Cornerstone matches up well into many of Rillaboom's counters (Moltres and Zapdos specfically), while allowing Cornerstone to take advantage of Sturdy multiple times. Those are the only offensive tools on this team, but like Srn mentioned others such as Life Orb Zama also benefit greatly from terrain.
This idea that Rillaboom is bad is overblown and absurd, as it still has a place in SV OU. Even though we are seeing a meta trend consisting of more and more mons which have better matchups into Rilla, that does not mean Rilla has no place. It is still unarguably the best terrain setter in all of SV, and the utility for which it provides cannot be replicated by any other mon. I think what limits people is their narrow assessment of Rillaboom. People force it into the archetype of wallbreaker, restricting it's moveset when in actuality it's toolkit is more suited to a supportive mon. I still firmly believe that Rillaboom and Grassy Terrain are under explored, and that with genuine innovation we could see Rillaboom rise back to prominence.
The utility and support Rillaboom provides is unmatched. With Terrain Extender, it can provided consistent chip healing for a majority of games, allowing for mons who otherwise would run Leftovers to run other items, and providing a larger window of opportunity to for those who rely on Grassy Seed. Additionally, another added benefit of Terrain Extender is not locking Rillaboom into one move, this allows Rillaboom the ability to either use Knock Off to make progress or Wood Hammer to significant damage, and then U-Turn out. Moreover, certain Pokémon who are normally faster than Rillaboom get lulled into staying in believing Rilla to be locked in either Knock Off or Wood Hammer, meaning it can get a jump on them with Grassy Glide and collect a surprise KO. Grassy Terrain as a supportive tool is unmatched, and provides so much to any time.
Not only does it provided meaningful chip healing as mentioned prior, it also enables a many offensive tools. For example, Hawlucha greatly appreciates the presence of Grassy Terrain, as it provides it with +1 Def as well as activating Unburden. With this Hawlucha with proper investment can be suprisingly bulky, living moves it would not normally otherwise, such as Ice Shard from Weavile. Hawlucha also handles many of the threats which unbanded Rillaboom thuds into, such as Zama and Kingambit. In a similar vain, Raging Bolt is amazing with Grassy Seed and Grassy Terrain support. With proper investment and the +1 Def from Grassy Seed, with full HP Bolt is able to comfortably live Headlong Rush from Great Tusk, and revenge kill it. Grassy Seed provides enough bulk that it pushes Raging Bolt out of the threshold of many certain kills otherwise, and the residual healing gives Bolt surprising longevity. Lastly, arguably the biggest beneficiary of Rilla's Grassy Terrain is Ogerpon. The additional power provided to Ogerpon's Powerwhip is invaluable. Grassy Terrain makes getting certain kills significantly easier, allowing for unboosted whip to OHKO some standard Ting-Lu sets, 2HKO standard Dondozo, and provide more favoruable rolls on Stall and BO regulars such as Gliscor, Clefable and Clodsire. With the presence of Grassy Terrain, Ogrepon becomes a ludicrous wallbreaker, synergizing extremely well with Cornerstone, as Cornerstone matches up well into many of Rillaboom's counters (Moltres and Zapdos specfically), while allowing Cornerstone to take advantage of Sturdy multiple times. Those are the only offensive tools on this team, but like Srn mentioned others such as Life Orb Zama also benefit greatly from terrain.
This idea that Rillaboom is bad is overblown and absurd, as it still has a place in SV OU. Even though we are seeing a meta trend consisting of more and more mons which have better matchups into Rilla, that does not mean Rilla has no place. It is still unarguably the best terrain setter in all of SV, and the utility for which it provides cannot be replicated by any other mon. I think what limits people is their narrow assessment of Rillaboom. People force it into the archetype of wallbreaker, restricting it's moveset when in actuality it's toolkit is more suited to a supportive mon. I still firmly believe that Rillaboom and Grassy Terrain are under explored, and that with genuine innovation we could see Rillaboom rise back to prominence.
@ Heavy-Duty Boots
and 
in non-stall matchups) while the combination of razor shell + knock enables it to outdamage most defoggers that are paired with gweez - be it 
or 
. It is important to give it free switches by playing aggressively and not get chipped early, since it does not have any recovery and its your primary anti-stall mon. Pairing this with 
@ Rocky Helmet
. Though it can function on its own, it is unstoppable when coupled with grassy terrain giving it more opportunites to set up on ground types. It can break through 
on it own which is the primary switch in on most stall teams as shown by the calcs below, and can potentially also bait a tera dark by feigning psyshock. Tbolt lets it pressure 
with haze, 
with AV and Spdef 
.
. thing is heinous with support. there's also, wait for it...stealth rock! wow!