Gross’s niche it compresses a psychic resist, xern check, and offensive presence into one pokemon, and unlike solgaleo doesn’t suck at it. With that in mind, tapu lele offense seemed to be the best bet.
The majority of sets are standard, with minimal variation. Deoxys is standard 4 move set with magic coat to cheese opposing hyper offense leads. Groudon is a 4 attack set with rock tomb and solar beam to pressure groundceus and waterceus, as well as maintain coverage on ho-oh and kyogre, all of which gross hates. Metagross itself is a standard 4 attacking set: meteor mash and zen hit hard under terrain, ice punch and eq hit flying targets and groudon respectively. Tapu lele is the standard set with terrain extender to keep powerful Zen headbutts, and remove priority like ygod’s sucker. Speaking of which, scarfed ygod matched up well as a revenge killer, and isn’t reliant on priority unlike the life orb set, making it ideal for psychic terrain. Finally, a groundceus with ice beam fits best because other arceus forms like ekiller or ghosteus clash with lele, and having two ice moves means zygarde will struggle to be at full health.
Not the best showcase per se but definitely fun, and covers a good amount of the meta :]