Thank you so much for tagging me on this topic Antar, I've been waiting for this.
Since a decent majority of the posts (not all obviously) seem to be on the "candle" side, I'm going to start making arguments for "not candle". Starting from earliest post to latest post.
1. No Item: This one is actually kind of tricky, because of the existence of one move and one move only, Knock off. Knock off deals tremendous damage to item holding pokemon, and a decent majority of megas not named venusaur are offensively oriented, meaning they'd prolly would rather not take a knock off, esp not repeated knock offs. I think that in this case, it may be worth it to run itemless on semi bulky pokemon or mons with reliable recovery such as Tornado-T or Skarm for the purposes of absorbing knock offs. This is very relevant to OU because Bisharp.
2. Megastoneless megamaw: It's a fairy steel with intimidate and pain split, meaning it
may be able to function as a phys wall. It also gets foul play. Feel free to debate me on this one, but I think that's a largely unexplored possible niche for it.
3. Jolly Talonflame and offensive-ish smeargle have been addressed. I see no reason to elaborate.
4. Regigigas is a massively underrated pokemon, and here's why.
a. Slow start only effects attack and speed, meaning that regigigas' titanic 160/110/110 bulk is untouched. This kind of bulk is borderline unheard of for any normal type.
b. Even with slow start, regigigas still has 80 base attack and base 80 sp attack, which while bad is not unusable.
c. his support movepool is not bad, sporting things like block, gravity, weather moves, thunderwave, toxic, and safegaurd. It even has the bulk to use psych up for possible counter sweeping capabilities.
5. Grasswhistle has use on whimscott
6. One stat lowering moves: Wobb loves tickle (dunno if that counts as a single stat lowerer or not) Also, parting shot is very viable on smeargle and one of pangoro's only viable moves.
7. Air Slash Charizard does NOT count, it's his best special STAB and can be used situationally to get past flash fire mons and a few others. Also, it's more accurate then fire blast which is sometimes relevant.
8. first evo mons: There are a few semi-viable first evo mons due to FEAR builds and eviolite. I can't think of a good list off the top of my head.
9. Ninjask: Ninjask has one set that outclasses sclopede, his band set. Adamant CB ninjask has one of the hardest hitting u-turns in the entire game and outspeeds all but a choice few of the unboosted meta (outspeeds + natured base 130s, if only barely). As an added bonus, infiltrator has the ability to hit through subs, which is very relevant against the likes of sub-CM latias and sub trenevants.
Quick calc just to show off how strong his u-turn is.
252+ Atk Choice Band Ninjask U-turn vs. 252 HP / 0 Def Latias: 320-378 (87.9 - 103.8%) -- 25% chance to OHKO
+1 4 Atk Genesect U-turn vs. 252 HP / 0 Def Latias: 288-342 (79.1 - 93.9%) -- guaranteed 2HKO after Leftovers recovery
And it ignores subs, so that's a guaranteed ohko if used after subs.
10. Fly, unnerve ttar, soundproof snow have been addressed. I see no need to comment on them
11. bite Gyara: I actually don't have much of a problem with bite gyara being a candle, I can't think of a good reason to use it besides flinch hax. Hitting trenevant maybe?
12. FF ninetails is outclassed by both unmega and mega houndoom, nothing wrong with that being a candle imo.
13. flying charge moves: Sky Attack w/o power herb is prolly bad, bounce is def not a candle due to para chance and lack of flying physical STABs. Fly is prolly also not a candle, but I don't have a strong argument one way or the other.
14. confusion causing berrys are definitely a candle
15. I'm going to go out on a limb here and say that protect is a move that never has ZERO competitive value. It is a useful scouting move that assists in figuring out your opponent's moveset with relatively little risk to the user. In a meta filled with stupidly hard hitting threats that can come out and deal heavy damage to punish even the slightest of mispredictions, I'd say it has competitive value. Also, defensive megazards exist, esp megazard-x with his phenomenal typing.
16. Tflame has some serious baron movepool syndrome, especially CB talonflame. Steel Wing is prolly just being used as a filler move due to a complete and utter lack of better choices. If you can find a fourth move to take over steel wing besides maybe roost or WoW (lol CB support moves), I may reconsider.
17. Azu resists both fire and ice, so thick fat azu is prolly a candle just because it doesn't have any trouble taking those moves in the first place.
18. Not entirely sold on payback ttar having no competetive value. It's pretty slow, so min speed ttar could be used to better break certain walls such as skarm.
19. SE coverage on chansey? Not entirely sure on this either.
20. Scarfed Bisharp can be used to revenge a few boosted priority threats like boosted mega pinsir and tflame (can "outspeed" normal bisharp's sucker punch) as well as boosted mons that resist sucker punch like terrakion.
21. Yeah, screw synchronize espeon
22. Effect Spore Breloom: I was gonna argue this, but I'm pretty sure it doesn't work thru subs and breloom can't take enough hits to get it to proc anything resembling reliably. So yeah, it's a candle.
23. Black Belt cuz you dislike LO recoil? Maybe not the best reasoning, but sharp beak tflame and water plate azu are things, so whynaut?
24. Agreed on spike cannon anything
25. Neutral Natures: Can't think of a single instance where I would use one except for simply forgetting to set it (I think we've all done that). It's a candle.
26. Pluck is not a legitimate reason to run confusion berries, bug bite maybe slightly moreso due to scizor. Trick users have better things to cripple their opponents with like flame orb and scarf.
27.
Agent Gibbs Here's why ur politoed argument fails, there are blatantly superior mons with water absorb, like Jellicent (who has most of toeds moves and more), vaporeon, and even Mantine. It's a little more difficult then you are implying (not much though, and it's not supposed to be).
28. specific status condition curing berries: What if you really hate one status condition but don't mind the others? For example, outrage mons prolly don't mind toxic, but they hate the self inflicted confusion, so persim berry would be nice. Also, I know you didn't mention it, prolly on purpose, but chestorest is a legit thing.
29. shell bell: yeah, can't think of any good reason to use it. It's a good concept, but the numbers are just too dang low.
30. inner focus bisharp: granted
31. Big Pecks Mandi: overcoat is better for anything except fighting tickle wobb, and taunt works better for that anyway.
32.
Ketsuban You are making the same fallacy
Agent Gibbs made with his toed statement. Don't look at mons in a vacuum, compare it to other mons. So you want to use sableye for negetive priority payback? Try lagging tail ttar, hits harder, more bulk, and can fling it later.
33. Evioliteless NFEs: I actually agree on this one. You may make an argument for evioliteless chansey, but at that point just use blissey.
34. Fringe uses for poison point and swarm scolopede: Focus Sash is a thing, making both of these semi worthwhile. Scolopede is fast enough, so it's worth considering (swarm moreso then poison point)
35. doubles abilities: prolly candles, unless no other abilities are available
This is taking much longer then I thought it would. I'll be back on later tonight, cya guys.