Type: Null: A decent mid-tier pick. Choice Band and Swords Dance sets seem like its bread and butter. It's a bit inconsistent with many offensive and defensive checks to it existing, and its defensive presence is not great despite the Steel typing. The saving graces, in my opinion, are a decent speed tier vs. balance teams and very punishing U-turn. I wouldn't be surprised to see Scarf becoming a set.
Crobat: This pokemon's great bulk and access to Magic Guard make it look promising, but its role in the meta is uncertain to me. As a wall it loses to Pupitar, Rotom-Mow, Farfetch'd, and Dugtrio, (just on the physical side) while beating Type: Null, Magearna, and Purugly. As a defensive Defogger it loses to Dugtrio, Pupitar, and Heracross, only stopping Torterra. It may have other niches by utilizing Taunt + Super Fang together with its good speed, or abusing Life Orb + Magic Guard to make up for its low offenses.
Galvantula: A really solid pivot. The ability to outspeed most of the tier makes it a nasty Toxic staller and lets it click Volt Switch for free in many situations. It's good against several pokemon both offensive and defensive, which is what makes it pretty reliable. I don't have much experience with Specs ( outside of the Thunder set I posted ) but I think it has potential. Dugtrio is its natural predator.
Dugtrio-Alola: Another fast support pokemon that can range from bulky to full offense. It's the fastest pokemon in the tier and the only Spiker; it also has Intimidate and a great defensive typing, letting bulkier sets switch in multiple times. It seems very solid right now; it doesn't have a lot of sheer power or bulk, but it can do its job of setting hazards, checking some pokemon, and stallbreaking very well.
Ludicolo: Ludicolo's place in the metagame has changed a lot with its nerf and the introduction of Wailord. I think offensive Rain Dance is definitely its best set now, with defensive sets being overshadowed by Wailord, who also deals with Ninetales but is a lot bulkier.
Rotom: Another pokemon that received recent major changes. With Levitate and the removal of Guts from Pupitar, it can now burn the two pokemon who used to turn it into a liability: Pupitar and Purugly. Recover is also a big deal; Rotom is a valid defensive threat now. Work Up sets have potential too but are fairly unexplored so I'm not sure what to say about them atm.
Torterra: Kind of a niche pokemon right now. It's the most solid Pupitar answer there is, and has a decent time setting Stealth Rock for a team. It's also the only way to set sun for Ninetales. It's held back by many weaknesses and terrible STAB typing. A Choice Band set is pretty decent too, as it still checks physical attackers and has good coverage.
Dragalge: Pretty underrated in my opinion. It's the tier's sole Toxic Spiker, has solid mixed bulk and a great defensive typing. Dragon Tail goes a long way towards keeping it from being passive, and it's Hydration+Rest set is good enough to be worth running with a couple of Rain abusers. Its low speed, lack of reliable recovery, and difficulty with Steel types keep it mid tier.
Ninetales: Thanks to good stats and great STABs, Ninetales is a high-tier pick that can run a lot of sets. It has a good speed tier, notably outspeeding Farfetch'd, which is part of why its Scarf set works. The variety of sets means that most teams need a defensive answer to it, not just checks.
Pupitar: Pupitar is a huge sweeping threat thanks to its Eviolite-enhanced bulk and powerful STAB EdgeQuake. Outside of dual-STAB and Dragon Dance, it has a "free" moveslot that can be used well for Stealth Rock, Toxic or a coverage move, or Rest to abuse Shed Skin. Its typing leaves it with many weaknesses, which in combo with its low speed can leave it highly pressured by the opposing team. However, there's no denying that it can win games on the spot if it finds the right opportunity to Dragon Dance.
Farfetch'd: A really solid wallbreaker or Scarf user. Defiant Scarf is very consistent and probably a good pair with Spikes Dugtrio to bait Defog. It's definitely one of the go-to scarfers. Stick + Sniper is basically unwallable as Cross Chop is guaranteed murder to non-resists and its coverage moves have a 50% chance to get a 2.25x boost as well. Well-played on VoltTurn it should dismantle the opponent. It's a bit of a glass cannon, and if you don't get your crits it can fall flat, but it's really scary.
Purugly: I'm not sure what to say about this as it was pretty heavily nerfed recently. It was an absolute terror despite only 90 base Atk due to incredible STABs that were covered perfectly by Stomping Tantrum. This together with good bulk and Regenerator and high speed left it with very few weaknesses. It now has less power and no Stomping Tantrum, and is a bit less bulky. It also no longer can switch into Rotom without fearing Will-o-Wisp. I wouldn't be surprised if the same sets still work, but I'm not sure yet.
Kyurem: This thing is an interesting pick but a bit inconsistent; it has good bulk, but only one resistance ( which is only relevant for walling itself ). It has good SpA, but poor coverage and no boosting ability. Still, a special attacker that can break Wailord, Ludicolo, and Dragalge while stalling out Umbreon definitely has its uses. Wailord makes a great partner as it can join in on the Pressure stall and heal it up with Wish.
Rotom-Wash: A very versatile pokemon that is equally at home being a wall as a wall breaker. It's a good Defog user thanks to a good matchup vs. Dugtrio and Pupitar and a decent one vs. Heracross. Offensive sets work because of the power of Hydro Pump and because both Water and Ghost are good STABs in the tier. 76 is actually a decent troll speed tier getting the jump on Heracross and Malamar. Taunt and Pain Split help it chip away at pokemon who can take its attacks.
Umbreon: Umbreon is a decent special wall that sports great bulk and only one weakness to Fairy. Merciless makes it a big threat to anything that it can poison, which allows it to apply some pressure. However, it has a hard time dealing damage if it can't poison the opponent, and its niche as a Wish passing wall is somewhat overshadowed by Wailord. Physical attackers don't have much trouble with it if they can dodge Foul Play.
Heracross: A very interesting pokemon that provides a lot of support in Stealth Rock, U-turn, Will-o-Wisp, and status immunity. All of these make it a pretty consistent choice for a Stealth Rock setter. Its pitfalls are its weak STABs and poor special bulk, which leave it with a choice between its damage or bulk being lacking, depending on EV's.
Magearna: Well I really don't know what to say about this as it was recently overhauled. It seems like the only candidate for a Trick Room sweeper, if nothing else, but I wouldn't be surprised to see other tank sets being successful.
Rotom-Mow: A pretty cool anti-offense pokemon. It has really good stats for a Shift Gear user, easily fitting a bit of bulk and an Adamant nature into its EV spread. Its coverage of Grass/Psychic/Steel is kind of awkward, as is its defensive typing, which leave it vunlerable to Galvantula and Heracross, as well as Steel types. I don't think it's a great spinner but it might still be worth using Rapid Spin on a Spikes stacking team.
Malamar: This pokemon's typing works very well for it, but this is balanced out by mediocre stats. All of its sets have trouble with Umbreon, while Happy Hour has trouble dealing damage in general. I suspect Happy Hour is not really its best set, and that sets like Sub+CM and Specs are more consistent due to their ability to have an impact prior to the late game.
Wailord: The new arrival, and it's been proving itself to be a beast. Wall sets are very good as Hurricane is threatening even with no EV's and its bulk is really off the charts by the tier's standards. Walling Ninetales is a great asset. I've also seen offensive sets work due to the power of its STABs. In all honesty it's probably a bit too strong, due to the combo of bulk and offensive presence; something has to give between those two.