Moves
Charm and Confide are used to neutralize Pokemon that will struggle to KO Gothorita with reduced damage output.
While Gothorita can easily overcome status with Rest, Taunt is still used to force attacks from trapped foes and make their attacking moves' PP diminish more quickly. Taunt also comes in handy for Gothorita in an event where it traps a Pokemon that it can temporarily shut down but struggles to outlast in the long run, such as Ferrothorn, which will struggle to punish a switch-in once Gothorita cripples it with Taunt and switches out.
Rest is used to give Gothorita a way to overcome repeated attacks from trapped foes and status ailments.
Though it is difficult to fit, Heal Bell is worth considering to let Gothorita support its teammates even more and be more useful in an unfavorable matchup.
Set Details
Maximum investment in HP and Special Defense with a Sassy nature improves Gothorita's ability to take special attacks from Arceus formes and notably enables it to switch into Choice Scarf Xerneas and neutralize it. Minimum Speed is used to take minimal damage from Ferrothorn's Gyro Ball, and this is hardly detrimental, as Gothorita is slower than Celesteela anyway.
An alternative EV spread of 252 HP / 112 Def / 144 SpD can be used to enable Gothorita to trap defensive Ho-Oh while still avoiding the 3HKO from support Arceus formes after Stealth Rock.
Usage Tips
In order to neutralize foes, switch Gothorita into weaker attacks like support Arceus formes' Judgment and any attack from defensive Ho-Oh and repeatedly use Charm or Confide, Taunt, and Rest to deplete the PP of all attacking moves from the victim. Trapped foes will eventually run out of their attacks' PP and will start to use Struggle until they faint, which can be completely taken advantage of by Gothorita's teammates.
As Gothorita will rely on PP stalling to neutralize a foe that it traps, make the best use of moves like Rest, which can potentially buy 48 turns, and Confide, which has just enough PP to stall out Calm Mind from Arceus formes.
Though Gothorita's bulk is superior to Gothitelle's, it will sometimes have to be more cautious about directly switching into attacks. An opponent may make double switches if they want their defensive Pokemon away from a hazardous situation, and entry hazards are going to punish Gothorita with every misprediction. Also, losing momentum can result in varying consequences.
This becomes less of a concern against slower teams, however, as many Pokemon that Gothorita can't necessarily trap cannot pose an immediate threat on Gothorita's switch. Slower teams also have many Pokemon that reliably switch into threats that they can reliably check, so this improves the odds for Gothorita to successfully trap problematic foes.
Against other teams, Gothorita can switch into support Arceus formes and potentially Choice Scarf Xerneas and defensive Ho-Oh as well. Being able to trap the latter two depending on EV investment can be particularly useful; Xerneas will refrain from using valuable utility moves like Aromatherapy and Defog, and Ho-Oh will think twice before attempting to spread Toxic or use Defog.
It may be tempting to make a quick move to eliminate passive foes for Gothorita's teammates, but patience will be an important factor for successfully using Gothorita. Depending on the rest of its team, Choice Scarf Yveltal locked into Oblivion Wing or defensive Necrozma-DM lacking Solganium Z or Swords Dance may have to be removed first. Scouting early-game will also generate an opportunity to observe how an opponent behaves against Gothorita paranoid opponents can be pressured into making predictions with Pursuit trappers like Tyranitar and Alolan Muk at a certain point, while a reckless opponent is more likely to be punished and lose one of their important Pokemon after a single misplay.
Have extra caution against Pokemon with Leech Seed. While Gothitelle will lose 1/16 of its health every turn because of Leftovers, Gothorita will lose 1/8 of its health every turn, making it less effective when PP stalling against Leech Seed users. Celesteela does sizable damage with Heavy Slam before Gothorita's Charm, and Ferrothorn beats Gothorita one-on-one with Bullet Seed and uses a lot of Gothorita's PP even if using another attack.
Most other Pokemon that Gothorita traps are easily neutralized by Charm and Confide. However, remember the amount of damage that Gothorita takes from the first blow, and if the next attack is going to weaken Gothorita enough to be taken out by a critical hit, use Rest. Although this may seem like an inefficient use of PP for a Pokemon that attempts to PP stall foes, Gothorita will likely outlast them anyway, and making passive foes run out of attacking moves is enough for its teammates to fully take advantage of them. As an example, Substitute users like Zygarde will have no fear against Taunted Arceus formes with no attacking moves left.
Team Options
Though Gothorita's usefulness is dependent on the opposing team, it can often trap and cripple at least one foe in many matchups. Support Arceus formes are seen on most teams due to their ability to blanket check a lot of Pokemon in the tier, so sweepers like Rock Polish Primal Groudon, Zygarde-C, and Mega Salamence can be considered. The synergy with Zygarde is going to be stronger if Zygarde has Thousand Waves, allowing Gothorita to immediately create a favorable matchup against a trapped switch-in.
Removing support Arceus formes can also benefit teammates like defensive Necrozma-DM, Ferrothorn, and an Arceus forme using Stealth Rock.
Teammates that can put in work against offensive teams can be helpful, as Gothorita will not likely have any foe it can reliably trap. Priority move users like Marshadow and Choice Scarf users like Xerneas and Yveltal can patch up this weakness, and Gothorita can trap many of their checks. Choice Scarf Yveltal is noteworthy for bringing in Gothorita safely with U-turn.
Consider employing an Arceus forme that will have some defensive presence. Using Gothorita can be hazardous otherwise due to the almost nonexistent defensive presence it has against any foe it cannot trap. Depending on the type, a support Arceus forme can be used to blanket check physical attackers or Dark- and Ghost-types. Any reasonable Arceus forme will appreciate Gothorita switching into Toxic and likely trapping the user, and they can be further supported if Gothorita has Heal Bell. If they are using Defog, they can swiftly remove entry hazards from Pokemon like Ferrothorn and opposing Arceus formes that may have set up while dealing with Gothorita.