Hi,
- As someone who wants to advance ORAS, I felt this would help both the competitive scene and more casual fun.
- I tried almost every mon here and I'm going to rank any mon with a semblence of viability
- I'm going to include an S+ rank
- Do not worry I did not write this in one sitting
- Since I'm still playing in WCoP, I will make my reasoning more general. Forgive me!
- S/o Amir for being a cool bud to build w/ esp with these lower mons
S+ Rank (Game Changing)

Serperior - The single best mon in the tier due to (1) its immediate presence on the field, (2) incredible speed tier, (3) its ability to absorb pressure from meta threats, (4) its sheer utility, and (5) versatility.

Diancie-Mega - The single best mega in the tier imo. It's hard to wall and magic bounce is one of the best abilities in the game.
S Rank (Consistently Consistent)

Alakazam-Mega - Everytime this mon is on the field the opponent has to make concessions. Focus miss to be missing tho.

Excadrill - Bossman

Clefable - High utility w/ LO sets being scary once again. Though a bit hard to punish steel types.

Weavile - Useful in every conceivable mu and punishes lazy teambuilding that lack good dark or ice resists.

Rotom-W - The 50/50s with drill in the back is always in Rotom-W's favor especially considering the fact that Rotom lives Drill's EQ
S- Rank (Slurp Slurp)

Lopunny-Mega - Somewhat of a fall from grace due to rise of static zapdos, but its utility is tremendous.

Tornadus-Therian - Just immensely useful in checking important threats like Serperior and Mega Alakazam.

Metagross-Mega - A year ago I would have put it like A- or A. Nowadys, its utility and versatility, along with its sheer bulk always coming in clutch, has put it back on the map for me ... I really like how this mon feels in modern meta, especially considering the top threats.

Volcanion - The best fire type in the tier and without a doubt.
A+ Rank (Where's Your Answer?)

Medicham-Mega - Probably the most slept on mega. Double prio is best to not be deadweight vs. offense.

Garchomp - Not only is RH rocks a very good glue but other sets like SD or LO 3 attacks are forgotten but very powerful threats.

Manaphy - I have 4 grey hairs and 3 of them are from Manaphy

Volcarona - the 4th one

Gliscor - A good Gliscor pilot and build will out last usual checks

Zapdos - The 2nd best flying type in the tier. Both static and pressure defog are amazing sets.
A Rank (Oh! The Pressure!)

Gallade-Mega - The bulky set is extremely hard to revenge kill and due to its versatile kit hard to wall as well.

Thundurus - Extremely useful and splashable mon

Keldeo - Keldeo is a paradox, the more its used the less its usefulness is due to its checks sprouting everywhere especially Jellicent. However when the meta shifts and the keldeo counterplay is Volcanion + Cofagrigus ... use this mon and profit. Also, its bulk comes in clutch vs. offense.

Charizard-Mega-Y - Hard to wall this mon and feels powerful on the field, but HP Rock Serperior sucks for it.

Tyranitar-Mega - Both DD and rocks 3 attacks - with pursuit or not - are massive threats

Bisharp - Strong threat on offense and incredibly good glue w/ AV on BO/Balanced

Slowbro - Not only a good blanket physical wall but can also be a solid wincon. However somewhat eclipsed by Volcanion

Cofagrigus - Toxic spikes are incredible and doubling as a spinblocker is insaneo. S/o
Vulpix03

Ferrothorn - Solid manaphy check and consistent spikes user
A- Rank (Suffocating)

Latias-Mega - Incredible utility and versatility but very pursuit and status weak

Tyranitar - Sand is too stable as an archetype

Landorus-Therian - A return to glory as its utility in keeping rocks up vs. drill teams is massive, generally great on offense.

Chansey - Never use chansey or blissey w/o status

Blissey - Worse before knock off but better after. Lefties toxic is slurp slurp, and extra speed is clutch.

Skarmory - Use Roar over Whirlwind, trust

Hippowdon - A rise from the low ranks due to its SpD set being a solid blanket check to many special threats like Volcarona, Zard Y, Mega Diancie, Thundurus/Zapdos, and so on. Keeping rocks vs. drill teams is incredible as well.

Dragonite - From typing to stats and ability, it is a solid wincon that also prevents offense from being swept.

Heatran - Somehow feels annoying to play against but also easy to chip. Quite useful vs. Clefable or Serperior but it's a fire type and a steel type that doesn't properly check Mega Diancie, Mega Alakazam, Volcarona, Zard Y, etc. so feels a bit lackluster for me.
B+ Rank (Very Solid)

Venusaur-Mega - Serperior & MDia check + tspike absorber + knock off is a great kit. Thick fat allows it to be a very good Manaphy check, and growth sets are genuinely scary for fat. Its main downside is status and Synthesis.

Talonflame - A fire type that I often prefer over Heatran since it actually checks moth and zard Y.

Amoonguss - Serperior & MDia check + tspike absorber + regen + spore is great, however deadweight vs. manaphy really sucks.

Seismitoad - Rotom infinite check glitch and also checks MDia and keeps rocks vs. drill. Unlocks 50/50s w/ double immunity.

Cloyster - Spin on offense is just too useful and always a threat.

Scizor-Mega - Solid MDia, MZam, and non-HP Fire Serp check cannot be underestimated. Though Zapdos/Volcanion are everywhere.

Gardevoir-Mega - Bulky Modest is the way to go.

Charizard-Mega-X - Goober Certified

Kyurem-Black - Bulky Kyurem-B should be used more often as its a solid Serp and Manaphy check.

Thundurus-therian - Sometimes 6-0s and sometimes is useless.

Suicune - See above + status weak, but pressure is amazing and the mon is overall much more versatile.

Kyurem - See above.

Cresselia - A better Latias as its a good blanket check physical or special, lunar dance > hwish, and actually lives knock/pursuit

Latios - The better Lati due to its immediate presence. Specs is scary and Scarf is incredible vs. offense.

Latias - Worse Cresselia but has speed, defog, and fire/water resist so has its places.

Gyarados-Mega - The single scariest mon on HO to face.

Altaria-mega - Heal bell is great for both offense and stall. A good longterm wincon, but really really hates steels.

Quagsire - This + Chansey is auto win vs. so many offense its crazy. Being a blanket physical checks to set up sweepers is incredible.

Gastrodon - I had this lower but tbh, Counter + Clear Smog is a very good and annoying set. It has its places for sure.
B Rank (Solid)

Mew - The best HO lead + stallbreaker sets are good.

Pinsir-Mega - Inconsistent af but it goobs

Slowbro-Mega - Weak to status. The more SpD you invest = the less Def = the earlier you have to mega = the worse it is. Solid wincon tho

Crawdaunt - Brazy mon

Scolipede - The amount of teams that are 6-0'd by this mon on preview is insane. Stomachs priority + Tspike absorber on offense is 10/10

Alomomola - On the rise for a good reason. Wish + Regen is far too good.

Gyarados - very underrated mon

Scizor - Regular Scizor is a strong CB user w/ pursuit, BP, and U-turn. Lefties w/ SD or Defog ain't bad either.

Gengar - Specs Gengar go pew pew, pair with something that takes advantage of pursuit.

Terrakion - Good speed tier and typing w/ immediate offensive pressure.

Infernape - Very good typing defensively to check dark types and fire types.

Azumarill - A Crawdaunt that is weaker but bulkier and w/o SD.

Tangrowth - A grass type competing w/ Seprerior, Amoonguss, and Ferrothorn for a slot ... if used, use RH + Brick Break
B- Rank (Somewhat Solid)

Aerodactyl - 2nd best HO lead but I'm sober on it now kinda.

Garchomp-Mega - Most underrated Mega. In Sand it's good and outside also good w/ 3 attacks mixed + Rocks.

Heracross-Mega - Strong boi that forces 50/50s concessions.

Latios-Mega - As an extension of how good Latios is, but with a mega slot. Unexplored.

Hydreigon - Decently explored but there's more. s/o
Always!

Victini - CB is good and Scarf final gambit alongside other sets are unexplored.

Diggersby - the new sets w/ AV or bulky SD are quite good imo

Reuniclus - Too many dark types but sometimes it goobs. The knock + T-wave set running around is pretty good.

Politoed - Rain is decently strong but toed is ass.

Kingdra - Fantastic rain abuser

Starmie - Garbage mon but we need spinners + it spins on tran which can be nice. Offensive is better.

Tentacruel - Kinda decent but no recovery or longevity sucks. Tspikes = Pog.

Jirachi - See Bronzong on typing + access to wish and other cool things. Good speed tier as well.

Magnezone - Excellent on stall, trash everywhere else as it forces structures that are hard to justify.
C+ Rank (Good but Niche)

- 3rd best HO lead

Aerodactyl-Mega - great in sand, s/o
Zaza

Swampert-Mega - great in rain

Camerupt-Mega - Good typing, pressures rocks vs. drill, destroys balanced, checks moth. S/o
DIYUSI and
Proftreez

Togekiss - 6-0s stall + cleric is nuts. Also can be a stall pick w/ Defog and Aura Sphere to punish bisharp.

Jellicent - Don't love it but it's annoying

Goodra - Strong check to Serperior and other special threats. S/o
Sylvi

Porygon-2 - SpD takes on MDia, MZam, Thundurus, etc. Can always take a hit from anything non-SE. Both Trace & Download are pog.

Empoleon - SpD checks moth one time, defogs on rocks Clefable, hits kinda hard, eats a hit from drill, flying check, good water resist.

Zygarde - the threat hidden in the valley of leaves.

Bronzong - Good typing that checks Serp, MDia, MZam, and even MMtgrs somehow, however pursuit weak. TR is underrated

Mandibuzz - bias pick but dark resist + MZam check is nice. Stall or sand pick.

Celebi - Unexplored

Raikou - Actually decent despite drill everywhere.

Nidoking - feels meh, offensive rocks or tspikes seems best

Breloom - Meh but s/o
devin , his loom builds scare me

Dragalge - checks Moth, Zard Y, Serp, Keldeo, and so on, while setting up and absorbing tspikes. s/o
Ithi

Forretress - spinner + rocks + spikes/tspikes. Good steel type. Unexplored.

Donphan - spinner + rocks and wins vs. drill, just w/o the fairy resist. Unexplored, mostly a stall pick.

Umbreon - wish + heal bell with good bulk and a dark resist
C Rank (Niche)

Manectric-Mega - meh, but lots of BO that rely on drill or chomp as their electric switchin can get goobed

Feraligatr - s/o
xray

Conkeldurr - AV goes in

Hawlucha - Unexplored

Hoopa - worse gengar double weak to pursuit, slow af, feels meh

Chesnaught - unexplored spike user and solid dark resist

Doublade - Permanent Medicham counter, stall pick. s/o
HSK7

Blastoise - spinner w/ refresh and scald aka spins on cofagrigus and drill. Unexplored, stall pick.

Snorlax - Unexplored

Aggron-Mega - Very underexplored mega

Abomasnow-Mega - see above

Milotic - Checks MDia, PP stalls clef, and solid water type. Haze, Dtail, Mirror Coat, Refresh all good. s/o
pj

Steelix-Mega - Unexplored mega. Stall pick.

Espeon - Unexplored

Cobalion - solid dark check + rocks + volt switch

Alakazam - Regular Zam w/ sash or LO is unexplored

Mamoswine - Looks good but is meh in practice. Too much Rotom-W

Crobat - sky plate infiltrator brave bird u-turn roost goes insaneo vs. offense.

Vaporeon - worse Umbreon

Ditto - Very hard to build w/, and tbh doesn't have the same utility it has in other gens

Magneton - I used to like the speed but honestly Zone is nice to pivot around Serp which this doesn't do as well.
C- Rank (Very Niche)

Uxie - Worse Azelf w/o Taunt but w/ Memento

Sableye - perma Medicham check and spin blocker. Stall pick

Chandelure - Unexplored.

Shuckle - hella meh. Sticky web is mu fish - aka inconsistent af

Masquerain - literally a better Sticky web user due to Intimidate & Hydro Pump, but doesn't have rocks, encore, etc.

Hitmontop - Stall pick spinner + dark resist.

Sharpedo-Mega - on some weird HO its fine

Drapion - Dark type w/ Pursuit + Tspike user/absorber + has SD. Multiple applications both on stall and outside

Poyrgon-Z - A bit too frail and/or too slow to do what it wants.

Flygon - decent defogger

Nidoqueen - Tspike user/absorber + solid ground type + rocks. Stall pick

Klefki - I dislike the keys. Aside from HO, I think its best on Stall.

Avalugg - Stall pick spinner that is weak to rocks and drill

Slowking - Mixed defenses is best but SpD Slowbro is just better due to its unpredictability.

Poliwrath - Keldeo typing is amazing defensively. Stall pick. Water absorb and circle throw with better bulk.

Metagross - mega bluff + AV pursuit is decent

Rotom-Mow - hard competing with serperior, but scarf trick is nice.

Roserade - Grass poison is a blessed typing esp w/ Natural Cure. Insane utility but very drill and pursuit weak.

Venusaur - same but with more bulk and less utility

Shaymin - Bulky grass w/ aromatherapy, and LO Seed Flare can stallbreak

Pangoro - 6-0 stall

Druddigon - Legitimately annoying and mold breaker rocks are nice. Glare is broken.

Lucario - Play guess the coverage with NP or SD and spectacular priority options. Frail af tho.

Heracross - one of the few mons I haven't tried, but on paper should be around here

Weezing - Stall pick. Tspikes user but doesn't absorb them which is unfortunate.

Kabutops - decent flying resist and spinner on rain

Ludicolo - decent rain abuser

Probopass - s/o ben gay. Stall pick. Trapper that traps Heatran.
D+ (Barely Viable)

Mesprit - Worse Uxie but w/ Healing Wish

Staraptor - Crack

Zangoose - Crack v2. Frail status absorber that abuses cofagrigus

Slurpuff - s/o Amir, almost beat me with it one time

Krookodile - Scarf moxie is nice

Salamence - DD set can be useful like 1 in 5 games

Aromatisse - Screens or TR that cannot be taunted

Miltank - Stall pick. Heal bell / rocks + sap sipper / thick fat can be clutch in checking important threats

Lanturn - Rotom and Thundy check + cleric + scald/volt switch

Gourgeist-Super - stall pick bulky ghost

Rotom-Heat - rotom that is weak to rocks but SpD checks moth ... except if its SubQD.

Moltres - niche defogger

Archeops - s/o
CrashinBoomBang

Whimsicott - Prankster encore = funny

Heliolisk - rain compatibile ability, electric w/ surf, and most of all, glare.

Omastar - shell smash is funny but even on rain 55 speed is just too bad.

Qwilfish - rain tspike abosrber and user, or spikes.

Smeargle - meme boi

Mienshao - Scarf reckless and hope you don't run into cofagrigus or clefable.
D Rank (Barely Viable Megas)

Absol-Mega - Frail

Beedrill-Mega - Super frail

Houndoom - NP can be scary if opponent is sleeping

Sceptile-Mega - love the mon but not it

Ampharos-Mega - a missed one

Audino-mega - maybe hypothetically possibly decent on stall

Blastoise-Mega - regular is better

Glalie-mega - has spikes ig

Pidgeot-Mega - not in this economy
D- (Almost Unviable)

Xatu - rocks drill is too popular and it can barely come in on Ferrothorn much less other mons.

Sharpedo - LO on HO be decent

Emboar - s/o Amir

Aurorus - Amir cooked me with this once.

Vileplume - Grass/poison but more niche. S/o Amir for SD Set

Toxicroak - nice on rain + tspike absorber

Registeel - can't keep rocks vs. drill but crazy stats

Rhyperior - too much drill and stuff

Audino - budget mola

Sylveon - budget Clefable

Virizion - Fast chesanaught but much worse

Ninetales - Highly dislike this

Barbaracle - why is this here
E (Pretty Much Unviable)

Lopunny - scarf switcheroo klutz mega bluff sheningans

Tornadus - ?

Mantine - nah

Entei - no shot