Buffs/nerfs suggestions:
Major need of buff: Abdelrahman, Alpha, Arby, Biggie, Perish Song, Pirate Princess, Raihan Kibana, Sectonia Servant, Zodiax
Could use a buff: Aelita, Awa, Billo, Celine, Estarossa, Piloswine Gripado, Rage, Segmr, Spandan
Major need of nerf: Andrew, Blaz, Hoeenhero, Rach
Could use a nerf: Arcticblast, Beowulf, Brandon, Gmars, Marshmallon, The Immortal
Reasoning + suggestions
Buffs:
Abdelrhaman reliably sets up trick room, but that's about all he does. Fire/ground coverage is ok, but with no boosting item, and no SpA investment, he doesn't hit very hard at all, unable to score KOs against a large portion of the meta, even with fully powered eruptions (which are often hard to achieve). I would recommend buffing either his power and coverage (e.g. replace The Town Outplay with Trick Room, replace Eruption with a kaboom-esque move, and add coverage in the place of Fire Blast), or his sustainability (e.g. passive healing or recover over fire blast).
Alpha suffers from basically the same problem he did before: Too slow, too frail, and doesn't hit quite hard enough to make up for it. My suggestions are to either make Ice Age a permanent ability (no need to use the Z-move first), or boost the power of Ice Age to 2x/Make Ice Age boost all of Alpha's moves (Plus replacing the 60 power Ancient Power with a slightly stronger option, like Power Gem) allowing the difficulty of getting Alpha in position worth the effort.
Arby is just a Keldeo with a low power priority move and a more accurate hydro pump. Expert belt is next to useless on it, as very few pokémon will stay in on a super-effective hit, and quickhammer will rarely find its mark, as most players know how to switch out. Wave terrain can be useful, but there's no guarantee it won't just remove your own hazards. In addition, Secret Sword means targets physical defence, which is almost always the wrong defensive stat for the targets it would want to hit (e.g. Rhydon, Pangoro, Archas, Aggron, Lucario). With no effective boosting item, Arby hits are not very strong. I recommend either increasing power (e.g. replace Secret Sword with Focus Blast + Wave Terrain boosts accuracy of fighting type moves too, more useful item such as life orb, choice specs, or a custom item), or making Arby an offensive support by making Wave Terrain only remove hazards on your own side, and possibly switching item to boots.
Biggie is just a Snorlax with slightly increased physical bulk, and a neat gimmick in assist. Snorlax is RU. Juggernaut punch very rarely finds its mark, as most moves deal more than 20%, and very few pokémon are threatened by Snorlax's uninvested attacks. I recommend either boosting Snorlax's power (e.g. Wicked Blow/Knock off over Darkest Lariat, attack investment (buff the ability to reduce all damage by 25% and replace the SpD investment), or its longevity (e.g. ability buffed to reduce damage more, replace a move with recover)
Perish Song is decent, if underwhelming compared to the other mons in the tier, but why is Trickery 85% accurate. There's no reason you should miss Trickery this often. You only get one good hit in most of the time, if that. If this is fixed, he would move up to the 'could use a buff' tier, where I would recommend Trickery hitting flying types, allowing you to use it with impunity, or adding an eviolite (or eviolite + helmet custom item or something) just for better tanking. At the moment, Perish Song can get worn down reasonably easily by the likes of HoeenHero, Aethernum, and Zodiax's hurricanes, which are pokémon this Rhydon should hard wall.
Pirate Princess is lacks the defensive prowess to set up, and lacks the immediate offensive power to threaten out opponents to allow it to set up to begin with. Combine this with the fact the setup is luck dependant, and the odds aren't in your favour, then you're not likely to get much done with this mon. The only buff I can think of that isn't too broken or too different from the original set is to give Dungeons and Dragons a higher chance to do something useful (e.g. 50% SpA, 50% speed, 30% random stat).
Raihan Kibana has decent defence, is able to outspeed opponents in sand, and can do virtually nothing with it. Weak offence, no reliable recovery, and poor STAB means he often comes in, chips an opponent, possibly knocks off their item if he can, then probably dies. He can sometimes go 1 for 1, but often fails to achieve that, and is thoroughly outclassed by almost every other weather mon. An attack boost in sand, making Stoutland normal/ground + replacing thousand waves with thousand arrows, and/or adding passive sand recovery (Ice body but for sand) to Royal Coat, or making Stoutland more defensively capable (e.g. Royal Coat = filter + current effect, or defence boost + current effect) are all potential buffs.
Sectonia Servant is too frail to effectively do what it hopes to do. Vulnerability to all entry hazards, all statuses, and a poor defensive typing, all mean that Sectonia can rarely set up, and frequently gets set up on. Pressure stalling moves is a neat idea, but Reuniclus lacks the ability to do so. In additional to all of this, Homunculus' vanity only has a 50% chance to raise the defensive stat you need it to raise. There are a couple of ideas that could help out a lot here: Innate Magic Guard, allowing Reuniclus to not lose to toxic, hazards, and being sat on by unaware walls; Buff to Homunculus' vanity, giving it +1 Def, SpD, and SpA, or healing 25% on use (while keeping the 50% Def/SpD, as I think both would be too much); or Homunculus' vanity sets trick room, in addition to its current effects (Although this may be too strong)
Zodiax is too frail to effectively set up, and too weak to effectively sweep. Often, in a best case scenario, you are able to get one quiver dance up, hit something for a decent chunk of its HP, then die. In a lot of games, the initial setup is almost impossible to get, and Zodiax dies without even landing a hit. Zodiax either needs a bit more power, or a bit more bulk. Giving Zodiax dry skin + Primordial Sea as an ability can help offset its frailty a bit, allowing it to passively recover while quiver dance reduces the power of special moves, and making it immune to water type attacks boosted by its own rain. Alternatively, you can make Big Storm Incoming slightly better by making Blizzard 100% accurate, and increasing each move's power to 40% of their original power, or by simply making it into Thunder Thunder Hurricane Hurricane, allowing the Zodihax to be less luck dependant.
Nerfs:
Andrew's previous nerf changed little. Specs STAB Moongeist beam from a 145 base SpA mon with one of the highest speeds in the tier is bad enough, but neutralising gas prevents most counterplay, as so many pokémon in the tier rely of their abilities (e.g. weather based mons, mons who boost their stats on switch-in), but honestly, removing N-gas alone wouldn't make Andrew that much more balanced. Spectrier can take most attacks in the tier at least once thanks to its great bulk, and whammer jammer is the icing on the cake, allowing this devastating wallbreaker to be an effective support for the rest of its team. Without a normal type on the team, you have basically no chance of stopping this mon if played well. It's too strong, too fast, and then even if you do happen to have the appropriate mon to counter it, it still has counterplay. For example, trick for Munchlax, or just a very powerful Pollen Puff for other normal types that might try and stop it. Even if you took away all of its moves apart from Moongeist beam, it would still be overbearing, because most of the other pokemon in the tier have no way to stop its assault.
As for how to nerf it, I think it needs some drastic changes. Remove N-gas, replace Moongeist Beam with Shadow Ball, and nerf Whammer Jammer so that either it doesn't remove hazards, or it doesn't deal damage, and replace Pollen Puff with Signal Beam, and I think Andrew will still be excellent, but much more balanced.
Blaz is the ultimate offensive-defensive mon. Low attacking stats don't matter when your attacks come off your 150-150 defences, and this is compounded by an immunity to toxic, a great offensive typing in fairy, filter, the ability to attack with an equally high attacking stat on the physical or special side, and access to an instant recovery move. Unaware walls cannot stand in its way, as even without boosts, it boasts those incredible 150-150 base stats, and cannot be worn down by toxic + recover. Removing either cosmic power or recover would be a good nerf (Possibly being replaced with refresh/lucky chant/conversion 2 and jungle healing/aqua ring/ingrain), allowing it to be worn down or preventing it from boosting to unkillable levels. Alternatively, changing its ability to something like battle armour, meaning that it can be toxic'd (but still maintains a useful defensive ability),
HoeenHero is in a similar boat to Andrew, in that it is very fast and very strong. The life orb recoil along with slightly lower bulk makes it a bit less broken, but Landfall's strength is staggering, and the speed drop allows it to support its team, or beat its potential counters with a guaranteed 2 hits as it comes in. Hoeen rarely needs to click other moves, but Hurricane means that grass types cannot stand in its way effectively. I recommend either moving the rain-setting to Landfall, meaning Hoeen must attack to set up, or reducing the power of landfall (e.g. making it a 4-turn slowdown for opponents guaranteed, but reducing its power to a flat 60 or 70).
Rach boasts an unimpressive 60 in every stat, and an unimpressive defensive typing. However, it is incredibly hard to stop, and reliably sets up hazards over and over during the course of a game, while statusing its potential counters. Spinda very rarely clicks anything other than Spinda wheel, mainly because of how busted it is. The best way to stop Spinda is a strong special attacker or a magic bounce user: However, the first is easily defeated by not switching Spinda in against them, or, if your opponent manages to accurately double switch in from a slower pokémon, hence avoiding the Burn it down, switching out. Magic bounce users are as perfect a counter as you can get, but they are few and far between, and only Quag can sit on Spinda forever: Hattrem and Azelf are worn down by knock off, and both dislike losing their item. There are other pokémon who beat Spinda one on one, but the problem is that Spinda doesn't come in on them: it comes in on one of the many pokémon it can safely do so against, then uses Spinda Wheel to safely scout, status, set up hazards, and heal, all at the same time. And, to top it all off, your pokémon will have had their offensive stats lowered, allowing the next pokémon to come in and attack more safely. The problem isn't that it's too bulky, as even after burn it down activates, there are quite a few pokémon capable of OHKOing it, but rather that it can abuse the many pokémon unable to do so very very easily. For how to nerf it, we can either remove regenerator, meaning that it must take time to actually heal (although this would honestly make Spinda very significantly worse), or nerf Spinda wheel, so that it either doesn't switch out the user (maybe replace another move with a switching move to make up for this), or a more minor nerf, such as taking away its ability to status, meaning that Spinda will set up hazards at the potential cost of inviting in a strong opposing pokémon.
This post is already massive so I won't go into the 'could use' sections in too much detail, but here are my suggestions quickly:
Buffs:
Aelita: Leftovers, maybe sub. Too easy to switch around currently, crippling weakness to toxic.
Awa: Too hard to set up sand safely, not always worth the reward. Sand rush + Sand force as ability, or maybe make sand into heavy sand?
Billo: Fishing for hacks is the only move you ever press, setting up is literally impossible. Doesn't really need too much of a buff, as hazards + knock off is good, but maybe a little passive healing or something?
Celine: Allow status guard to protect against special attacks (without statusing the special attacker)
Estarossa: Sand Balance = rocks + roar + teleport, or change stone edge to diamond storm, or gain SpD in sand. Currently too frail to effectively use as it has trouble recovering its HP back against the very strong threats in the tier with only HP investment.
Piloswine Gripado: Doesn't outspeed any offensive mons and is easily smacked without setup, especially on the special side. Either invest in a defensive spread and go for slow setup, or go offensive and invest in speed. Potentially add refresh's effect to icicle spirits and put a coverage move on there instead.
Rage: In Inversion terrain, pokémon cannot be prevented from moving due to paralysis. Losing because you paralysed yourself is not fun.
Segmr: Has difficulty surviving Tsukuyomi. Often deals 50% to the opponent then either switches, leaving itself on low health, or dies. Give it prankster, maybe (so it can recover before taking a second hit), or reduce the recoil from Tsukuyomi.
Spandan: Give Spandan some form of passive recovery. Currently suffers a similar problem to Segmr in that it toxic's the opponent, protects, then dies.
Nerfs:
Arcticblast: Very hard to kill. Remove priority on radiant burst, remove speed boost from radiant burst.
Beowulf: Disgustingly strong on first switch-in, can Buzz inspect later to clean reliably. Remove either Intrepid Sword or Adaptability.
Brandon: Hard walls any offensive mon, made worse by the fact special attackers go 0 attack for strength sap/foul play etc. Allow stat boosts to be applied correctly (i.e. Bane Terrain just applies a base stat swap, but swords dance boost will boost Earthquake's power), or maybe make bane terrain last 4 turns and remove terrain extender item.
Gmars: Very hard to wall after a successful shell smash outspeeds all unboosted mons, and hard to OHKO before a smash. Not sure how to nerf.
Marshmallon: Reduce Rawrrr heal to 25%.
The Immortal: A successful Watt Up often means the entire opposing team is going down. Either nerf coverage (e.g. Secret Sword replaced with energy ball), or nerf Watt Up (as suggested above, I like the idea of it using speed swap on pokémon who are faster than it)