im glad Genesect was sent to a farm up north, very obnoxious Pokemon to fight. Anyways here's the semi-weekly wall of text coming from God's most hardstuck 1100 player, but i am still having a lot of fun which is the main thing with this tier.
take whatever i say with a grain of salt, feel free to correct me on anything im wrong/unrealistic about. Also i dont suppose we care that much about giving megas fitting abilities so long as it isnt super "out there" and also makes it balanced.

(mega) i'm not gonna lie this thing with Regenerator is really obnoxious. It has almost no reason to not switch into non-Fire types and non-Flamethrower Clefable. Great defensive typing, absurd defensive stats, and good movepool to abuse all these qualities (U-Turn, Sucker Punch and First Impression in particular) makes him feel quite restricting on the teambuilder in a similar vein to Genesect. While Genesect's scarf+U-Turn sets make it quite a tall task to revenge kill, Mega Goli's bulk makes it an outright
Sisyphean task to KO. And its not exactly lacking in power either, where usually 1 or 2 Swords Dances is enough to allow it to stop all attempts to revenge kill with Sucker, and otherwise take out anything else with Iron Head since i find that anything that can OHKO/2HKO it gets Iron Head into oblivion. Regenerator allows Goli to come in and do as I said many times throughout a game, and its infuriating. I would even go as far to say that Annihilape (and Genesect when it was legal) is the only reason why these teams aren't dominating in a similar way that Skarm/Clef/Garchomp teams did.
I'm not sure what other ability would be balanced for it. Tinted Lens could turn it into Ultra Instinct Lokix, Tough Claws already exists on 5 megas, and of course, the pile of abilities that do nothing for Mega's like Long Reach and Sniper. The only abilities I could think of that
MIGHT help it define itself without making it oppressive is Heatproof. Heatproof, while leaving it only x2 weak to Fire, makes it a lot easier to chip down during a game, limiting the amount of oppurtunities it has to setup/force something out. It may also be worth trying Weak Armor, but i'm not confident in it because after a Weak Armor boost, it can outspeed even Talonflame at max speed investment.

(mega) Okay, ive had my fun with this guy. Now its time to address him. Adaptability makes Mega Golurk an absolute NIGHTMARE to fight in Trick Room. STAB Poltergeist allows it to OHKO, if not 2HKO most of the tier, and Close Combat deals with most Normal types that stand against it. Earthquake is just a generally strong move, with obvious exceptions. I've also seen people start to talk about running Rock Polish because after a Rock Polish, it outspeeds the Z-Megas at max speed investment. Giving it Analytic would force it to work with its low base Speed and nerf Trick Room teams and potential Rock Polish sets without completely neutering its power.
im still conflicted on ape, but im leaning on the side of ban. It can take many hits as its known for, but its also probably the reason why fatter teams aren't nearly as good right now, since Ape sits on these teams, which i do appreciate given how many Skarm/Clef/Chomp teams that were played pre-DLC. It also provides an alternative form of spin blocking to Gholdengo, and unlike Genesect, usually has 3 sets: Bulk Up/Taunt, AV U-Turn, or Scarf Final Gambit. Unfortunately, its offensive power means that it can be very difficult to switch into, and ive also seen other sets pop up from time to time such as Rest-o-Chesto, so it might have potential to expand its influence in the teambuilder more to the point of being too constricting. okay just kill this guy fr
ok bye